I’ve done this when younger and as a working adult and have my share of bad experiences.
So, working out how much it costs to board/lease/care for horse and how much she is getting paid and basically stick to that.
You can write it worth of each task or have an hourly wage, as other have said.
Make everything clear - written somewhere is best. When I was in HS there was a summertime “work to ride” program - 8 hrs of work meant one ride. The owners were shocked when I did 8 hrs of work in one day my first day. The other kids mostly just hung around.
So…to rehash…clarity is the best policy!
When I get upset, the first thing I start doing is the math. As a working adult, I also help people with training their horses/giving lessons. For that, I charged $30/ride. Where I boarded my horse, I fed some of the horses and rode at least one horse, almost every day.
I knew how much the owner charged for board and I would do the math - eventually that was one of my issues. I was getting way underpaid between 1.5 hrs at least 6 days a week feeding, then one ride at least 6 days a week…$10/hr for that 1.5 hrs is about $360/month and the rides were about $720 So that’s $1060/month. Basic full board at the place was about $30/day, or $900/month and my horse was field board. Even training board was $40/day, or about $1200/month and my horse wasn’t in training. Even if you added in my occasional (4 times a year or so) use of the trailer, I still didn’t feel like I came out even - add that to conflicting personalities and it was time to go.
This situation started out with less work and I paid some money in board but as it progressed to more work and I wasn’t paying board, that’s where the line started to get fuzzy. So don’t make that mistake - be cognizant.
I work of my board where I am now also, but there is much less grunt work, my horse is on a fancy organic diet, has a stall, and while I do work with the young horses, the entire atmosphere is more relaxed and I have not yet felt the need to do the math.