I think it is interesting to note that there is very little correlation between abuse (or rough handling) and a horse being hard to catch. That’s just not how horses think.
Horses that are shy or hard to catch most often come from a background where they were not handled as foals and therefore, as a prey animal, identify anything they aren’t certain about as a possible predator that should naturally be avoided. Horses are naturally shy creatures–like a bird or a deer–if they aren’t handled by humans when they are young. Horses that are introduced to humans later in life can easily retain a certain amount of suspicion or shyness or dislike of human company throughout their lives without ever having been roughly handled.
Other horses that are difficult to catch have simply connected the fact that being caught = being separated from friends/locked in a stall/put to work and that’s something they prefer to avoid. Horses like this are perfectly comfortable with humans–in fact they know us too well.
These are just generalities, but most horses with catching issues fall into one of these categories.
So, in sum, most likely no one has ever abused this pony mare. Teaching her to be caught is more about learning how to manage a behavior problem that she has, not about gaining her trust. If she didn’t trust people, she wouldn’t be able to do pony rides. It’s a training issue, not a trust issue. FWIW, fixing catching issues is a pretty advanced task, probably not a good one to take on as a beginner.
I’m confused by your motivation to want to spend time with this mare–who you don’t own–who seems to prefer being left alone. If I were going to suggest a starting place, I would suggest foregoing the catching and simply going out with a peppermint and a currycomb and doing a quick curry and snack without catching. However, if this were my farm I would not allow you to do this given that you do not own the horse, and also because working on horses that are loose in a field could potentially be dangerous for someone who is inexperienced with horses and cannot read their language/warning signals.
My real recommendation would be for you to find a horse to groom and handle that actually enjoys human attention. It seems to me that would be a win-win situation, as opposed to trying to solve behavioral problems that are above your experience level.
