I agree with all of that. I was just clarifying so a beginner rider understands the difference, if they’re reading this thread.
I’m not sure what resources the OP and her family have, or how much autonomy or choice she gets in her lessons or health care. From the details, I’m thinking these could be fairly low-priced, possibly lowish quality, group lessons and maybe there aren’t resources for more help. In that case, the do it yourself fixes are a really good starting point.
If there are some extra resources around, though, I don’t see why the OP can’t have an individual longe lesson a couple of times in addition to the group lesson she takes with her mom. A long lesson could just be 15 minutes hard work after or before the group lesson; you wouldn’t want to longe a horse for an hour.
As far as a chiropracter, IME they run $75 to $100 a session. Most employer-paid health insurance plans carry some amount of coverage for body work (chiro, massage therapy, physical therapy) because these are so effective at getting employees back to work after back injuries, etc :). You might need to get your family doctor to refer you in order to be covered. If you truly aren’t covered, and money is really tight, then obviously this isn’t possible. You could also get your family doctor to examine you for inbalances, which would be covered, I assume. But if there is discretionary income, spending money on chiro is money well spent, especially if you can catch a skeletal inbalance now, when you are young enough to try to fix it, rather than when you are 45 and your back is extremely painful.
The other component is miles in the saddle, including riding bareback and without stirrups, walk and trot. As I suspected, the OP is a beginner, still trying to get her balance, and I would guess that there are other posture problems. Maybe tipping forward, or leaning too far back; certainly relying on stirrups for security. Without talking to the instructor and watching a lesson, it’s hard to know what the instructor is prioritizing. Instructor may still be working on just basic comfort on the horse, and not putting too much emphasis on position. Or instructor may not have much to offer in terms of analyzing position.
I’ve recently watched a complete beginner start longe lessons with a very good instructor, as a favor to me, and it was eye-opening to see how fast the beginner developed balance and a decent seat with excellent, focused instruction. I always assumed that when you learned to ride, you learned to ride badly, and then after a few years if you got serious, you went to lessons and tried to unlearn all your bad habits 
(I learned with no instruction at all, as a teen).
It’s too bad that (IME) many instructors of beginners are not particularly good at teaching position and seat, and just let the students bounce around anyhow.
It is also very possible, as other posters have pointed out, that the saddle fit is less than excellent on the lesson horses.
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It’s too bad that (IME) many instructors of beginners are not particularly good at teaching position and seat, and just let the students bounce around anyhow.[/QUOTE]
Amen, to that!
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It’s too bad that (IME) many instructors of beginners are not particularly good at teaching position and seat, and just let the students bounce around anyhow.
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In fairness to some instructors of beginners,
I once commented to an assistant trainer on a beginning lesson that I observed being given by a working student at a public stable. It was a western lesson given by someone that didn’t ride western. The student was riding with romel (row-mel) reins that were a mile too long between her hands so that the loop narrowly avoided getting caught on the horn with each stride with her incorrect hand position. Fortunately, the horse was barely moving so there was no great danger despite the WS repeatedly telling the rider to “hit him with the Rommel.” Absolutely no instruction related to proper position of hands, seat or legs. And no German field marshall either.
The assistant trainer knew better but when I expressed concern about the quality of instruction she told me “some people don’t really want to learn to ride, they just want to sit on a horse.”
My lessons are a semi-private type thing, it is me and my mom in the lesson only. I talked to my coach today, and she said she would be willing to do lunge lessons with me. I will probably get a lunge lesson tomorrow.
Remember it isn’t just being longed that does the magic
The idea is that, on the longe, you can forget about needing to steer the horse, and you can let the reins loose so you aren’t using them to balance. So you can concentrate on your seat, ride without stirrups, etc.
But the longe lesson will have a lot more impact if your coach is able to diagnose the source of your position problem and give you exercises to fix it. Guaranteed, the problem you describe is not in the right foot or ankle, and may not even be in the right side of your body (lots of posters have given you good advice on this)
Remember it isn’t just being longed that does the magic
The idea is that, on the longe, you can forget about needing to steer the horse, and you can let the reins loose so you aren’t using them to balance. So you can concentrate on your seat, ride without stirrups, etc.
But the longe lesson will have a lot more impact if your coach is able to diagnose the source of your position problem and give you exercises to fix it. Guaranteed, the problem you describe is not in the right foot or ankle, and may not even be in the right side of your body (lots of posters have given you good advice on this)
So you’ve gotten some great advice for on the horse exercises (and some off), and here’s my contribution:
Go ride your bike (if you have one). Seriously, pay attention to how you are sitting on the bike saddle. Is your weight distributed evenly between your seat bones? If you take your hands off the handlebars for a few moments, can you cruise straight on? If not, you’ll figure out pretty quickly if you are sitting heavy to one side. 
Work on your body awareness - pedal and think about leading with the right leg for 5 rotations, then the left leg for 5 rotations. Seems simple, but trust me, it’s not. When you stop and put a foot down, alternate between your left and right. I’ll bet you have a harder time on one side. I know I do. It’s little stuff, but it does carry over to riding.
Also, should you find yourself sitting on a flat surface (like a countertop or something) - make yourself sit up straight and tuck your tailbone like you are in the saddle. It’s tough, but you will feel if you slump to one side.
It’s most likely because the horse is stiff left hollow right…he throws you into shortening your left side and putting your hips to the right, shoulders left and “carrying” him with your leg.
IMHO you need to learn to ride both sides of the horse correctly to fix the problem. School horses are often more crooked than the rest but they CAN be ridden correctly once you understand the bio mechanics of balancing the horse in the outside rein with inside leg.
post a picture if you can!
