Yeah, this seems odd. I really doubt she is in charge. And she would not be a Barn Owner. Sorry, had to clear that up. If her name is not on the deed, she is not owner. So basically she works for/with her parents and is trying to take advantage of her power.
Okay lets look at this a little bit. She gives you free lessons and you help around the barn. Why not just talk to her about it? Tell her that while once in a while you will ride one of her horses on a road ride you also want to take your horse sometimes. Set a goal for how many arena and road rides you want on your horse and how often you can help her with her horses. If she has too many to ride then maybe she should think about leasing them out, you could just gently suggest that.
Also if Diamond is so fat you might consider cutting back on the feed.
I think it can be worked out and yes if she is not reasonable have mom talk to mom.
Try to keep it friendly and it will be better for all. Do you have anyone else you can road ride with? Also riding different horses is really good for you too.
^^We don't give feed, just grass. No there is no one else to ride with it sucks haha. I know its good for me but I mostly ride her horses.I was training her green mare(she has only been riden 2 times) to be not spooky, (she spooked at barrels!!!) And I accomplished it. And it was fun, but she always want me to train her more when I go out there, but (1. I need to ride me horses (2.I can't catch her because she runs away from me.
Yeah she isnt the owner but it seemed easier to put it that was. But like I said she owns all the horses (not mine), deals with all the boarders, feed the horses, And all that.
Hmmm, you may need a grazing muzzle for Diamond. I can't remember the pics...I would just be firm and stand up to her then about being able to take Diamond out sometimes on the road rides....I am sure you can work it out.
With my luck the thing would fall off, because all the horses play halter tag so yeah. And usually you see horses when they are skinny to perfect. Diamond was skinny I got him FAT and then back down again but stll fat