This spring I bought a young pinto draft filly. When I first went to visit her, (before purchase) she was extremely fearful of anybody approaching her. She had'nt been handled much, (not even stabled) except for veterinary visits and once with a farrier.
When I brought her home she was still afraid of being approached or touched. So I spent the entire afternoon just hanging out with her, basically just being a horse. At the end of the first day she would let me rub her forehead, and scratch her neck a bit. The next day, she followed me into the barn and allowed me to put a halter on her, I did'nt have to trick her, force her or anything. Since then she has followed me around like a puppy. She will let me do almost anything with her. For example, I've only had her 2 weeks... today I gave her a bath, she stood and let me turn the hose on all over her, cover her with a wool cooler afterwards, and spray her from head to toe with conditioner.
The first week I had her, she was still nervous of people other than me. The last 5 days or so, she has started to act aggressive towards anyone else who comes into her paddock or tries to touch or handle her. She threatens to bite, and sometimes threatens to kick. (But has'nt done either yet.)
I should mention, that some of the people she has been aggressive towards are trainers and very experienced with horses. Whenever she acts like that, I tell her NO!, and make her back off, but that seems to make her even worse. I am finding it difficult to come up with an appropriate solution because she is not aggressive towards me, only other people. I don't want to her chased around a round pen, because I think it will put too much stress on her legs at this young age. Also, I think it is very important to nip this problem in the bud, as she just turned a year 2 days ago, but is already 14.2 hands and almost 900lbs.
I would greatly appreciate advice from anyone who has dealt with this type of situation.