Should I stop riding this horse?
I started riding about 10 months ago, once to twice a week. I recently started taking lessons at a new barn near my house; I've been there for about six weeks now. My first four rides, I rode an experienced mare twice and an experienced gelding twice. The last five rides I have been on a slightly younger (but experienced) pony. Because of my experiences on her, I think she might be too much for me to handle. On the other hand, I don't want to run away from a challenge if this is not a truly dangerous situation, especially since I think that riding this pony has made me a stronger rider.
The pony is generally sweet on the ground, though she has a few trust issues (she has only been at the barn for about six months, and may have suffered some abuse at her previous barn -- she clearly gets a bit nervous sometimes, though has never done something dangerous or scary during grooming/tacking), and she does NOT get along with other horses. She's very energetic in the ring, and a consistent challenge with her is getting her to stand still after I mount, or to slow down. When we are in a group lesson, she constantly tries to catch up with the horse in front of her, and it sometimes takes me half the arena to slow her down or stop her. This has happened at the trot and at the canter.
The first time I rode her, she was challenging but fun. The same was true the second and third time, though each time she had small spooks in the ring. The fourth time, she spooked while at the canter, and I flew through a jump. None of these really concerned me, because other horses spooked those days as well, and none of it seemed deliberate -- she just got spooked at an unfortunate location. I got back on her, and we had a good ending to the lesson, including some canter work. The fifth ride really scared me, though. She was trying to race the horse in front of us. Using half halts didn't work, so I pulled her out of the line and into the center of the arena where I worked on making her stand still, back up and walk small circles. When this was done, I got her back on the rail and started a posting trot. After a dozen strides, right when we went into the first turn, she took off at a gallop. I lost the stirrups and reins, and after the third turn flew off into the fence. I didn't get seriously injured -- just lost a lot of skin on my shoulder and arms and was sore for a few days. The instructor put her in a new, harsher bit and rode her for a few minutes, then had me get on just at the walk for a few minutes. I don't think she spooked before the bolt, but neither me nor my instructor know for sure. Because I had just disciplined her for not slowing down, I suspect she was acting dominant. The moment I fell off of her, she stopped galloping.
I didn't ride for another two weeks because I went out of town on vacation. I rode for the first time yesterday with a friend at my old barn. I was on an old gentle horse I've ridden before but was terrified the entire time. Today I return to the new barn, and suspect based on a phone conversation with my instructor that she wants me to ride the pony again. She said that this pony has never had such an incident that she knows of before (there are multiple trainers at the barn and she said she spoke to them), and that I need to learn to keep my horse's attention during the entire ride to prevent these incidents in the first place. I know that she's right; another rider in the class who has been riding there for three years says she never had any such problem on the pony. But I'm also afraid that this bolt was an escalation of the pony's previous behavior -- being extremely difficult to slow down or stop -- and therefore that it was not an isolated freak incident, but instead the pony engaging in a pattern of behavior she has learned I cannot effectively control.
If this seems like a problem that I should be able to handle and that will make me a stronger rider, I will continue riding this pony (I had been considering leasing her before this last ride; when she's behaving she's a lot of fun to ride). But I don't want to continue if this is a dangerous situation, and my gut (and friends) is telling me that I should ask for a different horse. I'm also afraid my trainer will look down on me for walking away from a challenge, and that by insisting on a different horse I will be jeopardizing my ability to progress as a rider. I also do not have much experience falling -- these two falls on the pony were my second and third falls ever -- and am concerned that my reaction may simply be fear-based.
Any advice is appreciated!