Well firstly thanks for all the replies!
To clarify a couple of things: It’s a win-win situation as far as Daisy is concerned—I don’t have my own horse nor the money for unlimited lessons, so I ride Daisy or school horses when their basics need refreshing (easy things, picking up the right leads, suppleness and transitions, etc…) and I get to ride for free 
This was certainly not a dangerous situation and nobody was delayed or threatened by my more subtle approach.
The only trainers that I’m aware of at this barn are the co-owners, whom I’m on very good terms with. However, the Busy Body definitely walks around like she owns the place and is an accomplished trainer, but due to the several horses she boards there, and thus large amounts of money she contributes, nobody seems to interject when she says something. I don’t have a vast amount of horse training experience, so I like to be open to suggestions and help from those that do, however, I hate the band-aid fixes (in this case, having someone stand there) that are all too common in sport focused barns.
I suppose I’m frustrated that I lacked the confidence to see my method through. I didn’t want to ruffle any feathers since, let’s face it, in a barn gossip spreads faster than fire, but in hindsight I guess I should have opened my mouth. How is it that my confidence doesn’t falter on a green OTTB on a windy day, but one annoying Busy Body has me questioning my abilities to even get on?? The human brain works in weird ways…
Ah the plot thickens. Is BB a horse pro, is she looking for clients as coach or trainer?
Some coaches will act like this imagining that you will be so impressed that you run to them and pay them money. Or if they know you are someone else’s student, they may act like this to compete with the other trainer or run you off the property
Regardless if BB couldn’t see what you were doing with the mounting block her training tool kit is not very full.
OP, you’re going to love it when you get older and no longer care (much) what other people think. It’s tremendously fun. But in the meantime, the phrase, “You’re too kind, but we’re fine as we are,” with eye contact and leadership body language (calmly, with quiet energy, take the two seconds to squarely face the other person and deliver your message – as many times as needed, the exact same wording each time-- and then wait for them to back away muttering), solves many a barn dynamic.
Sorry I’m not at your barn to take this on for you. 
At this phase of life, I eat confrontation like it’s a hot fudge sundae.
Yeah OP… there is a confrontation tolerance upgrade in your future but the price you pay is getting older. LOL I was thinking how this would totally have happened to me 30 years ago and how it would so not happen to me now. I would not react super well to this scenario these days…
When does this happen?
I can only speak for myself and I was probably a late bloomer on it due to my life before but turning 40 was a whole new 'tude.
I’m here, in my mid 30s. Don’t GAF. You don’t like what I do? Great, go away and don’t ever buy a horse from me or take lessons from me. Problem --> solved.
Having followed some of the trainwreck threads about your old barn… I think you got a crash course in Avoid The Cray Cray 
OP - let me tell you that when I told that trainer off, I was 19 and SHAKING afterwards. Now, I only get shaky when I’m darn mad . Sounds like this Trainer clocked you as outside her “accepted methods” and decided to make a scene for… whatever reason. Not the type of pro I’d be running to for help.
It was all good. You avoided unnecessary and useless confrontational conflict with a stranger. Daisy had to stand still whether held or not, either way she got the message to stand. The antagonist had nothing to fight against so the situation ended as quickly as it could and you could go back to riding your friend’s horse. Nothing dumb about any of it.
I do agree with those who voiced a concern as to letting someone unknown hold your horse while you mount. Even when you know people, that can be very dangerous if the horse takes a dislike to them and/or is ansy and/or spooks.
All in all, you handled the situation very well.
If this happens to you in future - “I do not need your assistance at this time. If I require assistance I will be sure to ask for help from (your trainer, or horse owner).” They try to persist “thank you, but I will be sure to ask for help should I need it. Right now, we are working through it on our own.”
I also like gracelikerain’s suggestion above. Polite, making it clear you have your ducks in a row, and everyone is in alignment - irrespective of what busybody sees/thinks. You are not her client. She is not on your payroll. It was not a dangerous situation. It did not warrant intervention, especially in the way she did it, setting herself up as the saviour/savant.
Posing it as you either being dumb, or needing a thicker skin is a bit of a fallacy - you are not dumb, nor do you need a thicker skin. BB needs to mind her own business (which she will not do naturally, some people just don’t) and barring that magically happening, practicing a few things/having a few comments rehearsed for the next time (if/when) this happens will help you advocate for yourself more effectively.
Well, I was somewhere in my 50s… Frankly, it started with getting my first horse (in my early 40s). Figuring out how to be a team with her, solving problems on the trail when it was just the two of us alone in the woods somewhere, buying a trailer and trailering just the two of us, seeing how she lived in the moment and then just moved on… I think this helped teach me. She was, however, an Arab mare and they are a higher life form than most. 
Or it may have just been a factor of getting older and/or learning the leadership that is required for raising children, because we had our kids when I was in my early 40s. Or because I changed careers and that was a good move, though I don’t know whether the confidence or the career change came first. Whatever. I am bad-ass now, if I want to be.
While I disagree with your (and several others on this thread) mounting block method, I think you handled the situation with the rude, presumptuous other rider very well. She had no business barging into your work unless you were in danger, which you clearly weren’t. (I also don’t agree with having someone, stranger or otherwise, hold the horse.)
I would have said something along the lines of why don’t you use the mounting block first ? I am working on something with this horse and it might take me a few minutes. That way they are not waiting for and watching you . It’s also is a way show them that you know there is an issue and that you are working on it . If they offer you any other help all you need to say is no thank you .
Also as someone that has horses in the past that couldn’t , for various reasons be held at the mounting block I would have been angry if anyone held the horse without my permission. That can cause big problems with certain horses .
I am finding 9 out of 10 times when I find myself nodding along and/or laughing at a reply it’s yours @Scribbler
I wish you were my neighbor 
OP… I’m old enough that I really should have learned by now not to GAF what some people have to say about any number of things (what I do with my horses, how I raise my kids, what’s going on in my marriage, how I spend my free time or income, etc)… however… sometimes stuff still gets under my skin.
I learned a useful technique a few years ago that I try and consciously employ in certain situations when I feel “stung” by a weird comment. When someone says something that sounds… unpleasant… I pause for 5 seconds, and then repeat back exactly what they said to me, but sometimes with an ‘Oh. Are you saying that I am blah blah blah…’ with a verbal question mark attached at the end. I try and keep the pitch of my voice in a pleasant, but questioning range… but keep my eyes locked right on the person who says the rude thing to begin with…
So here’s how it would have worked in your situation with the BusyBody.
BusyBody: “You’re screwing up the horse and she’s learning that she can do whatever she wants.”
OP: “Oh. I’m screwing up the horse and she’s learning that she can do whatever she wants?”
…
BusyBody: “Dearest Daughter, hold Daisy while OP mounts because she obviously don’t know what she’s doing and won’t ask for help when she clearly needs it.”
OP: “Oh. Are you telling Dearest Daughter to hold Daisy while I mount because I obviously don’t know what I’m doing and won’t ask for help when I clearly need it?”
…
BusyBody: “You should be taking lessons and not riding other people’s horses if you’re that inexperienced.”
OP: “Oh. I should be taking lessons and not riding other people’s horses because I’m inexperienced?”
Anyway… the whole technique essentially involves flipping the interaction back on the jerk. They can then either explain/soften their rude statements (sometimes people are just obtuse and clueless about how rudely they come across, and this technique is really useful with people like that)… or… they can mumble something and then stop it (a lot of blustery jerks will do that when calmly confronted in this manner)… or… they can double down and fly their jerk flag high for everyone to see.
The nice thing? You politely lob that ball right on back into THEIR court. So the unpleasantness is firmly THEIR responsibility to own and rectify… or not.
I was on a group trail ride on my little mustang and we had stopped at one point and I needed to dismount to adjust my saddle. When I went to remount, I stood on a log and my horse moved away slightly. Some BB piped up about how to straighten her out and to praise her when she moved back. Then she went to dismount to come over and hold her. At that point I swung onto her back and made her look like an idiot. I heard someone behind me tell BB “you know, she adopted that horse from the BLM as a yearling and trained her herself, I think she knows what she’s doing.”
The one thing that has stopped such incidents from happening to me has been–using a double bridle.
I know this was not your horse so probably not possible.
But so many people no longer use a double bridle that the people on the side-lines sort of automatically seem to think that what I do with a double bridle on is WAY beyond their knowledge base.
Even when I ride only at a walk and trot nowadays.
As a side note I have had zero difficulties with introducing horses to the double bridle, my own horses I trained, my own horses I was retraining to fill gaping holes, and now with lesson horses usually the first time I ride them, at a hunt seat stable.
If you ride at a Saddle Seat barn disregard this, they DO know how to use a double bridle.
Mt main response concern would have been addressed in the response “Don’t touch my horse.” Otherwise ignoring them. You did fine. Next time don’t let anyone touch your horse.
A bit off topic but still relevant; in an attempt to find out how other people tackle mounting with side-steppers, I decided to ask some friends. Someone sent me this video: https://www.youtube.com/watch?v=06wOO4T4pNo
Thoughts?
Bless that someone behind you. I wish we could all have someones behind us on these occasions.
