Pushy Yearling Filly

Ive Recently Brought a filly. we brought her because she was obviousley being mistreated and was underweight, she has had practically no human contact and the contact she has had was mean. In three weeks we've taught her to have a halter on ( she now comes to you to put it on) and recently started working on her feet and have succeeded with her two front feet. She doesnt lead correctly but were working on that. My main problem is she has started to be very aggressive and pushy, ad has even bit somebody, i dont want to hurt her or scare her but i want her to know im the boss. We have had the vet out and she says shes fine. My filly is a year old and already stands at 14.2 and is measured to make around 16.2, so even now shes big and is going to get bigger so we seriosuly need to knock this nasty behaviour on the head (Yes im sure it is nasty and not playful or loving, she has her ears pinned back). Other then this (which has only started recently) she is a lovley filly with a wonderful nature, she doesnt want to fight, i can see that most of the time, i just think nobody gave her the time she needed and it has greatly affected her. I feel like we've made brilliant process but now it just kind of stopped. Does anybody have any suggestion on either leading or the pushing around and nipping?
thank you

Let her know you have a spastic elbow. While you're leading her around, you can randomly flail your elbow around [without hitting her.] Eventually, she will think your arm is just totally possessed and won't want to bother it. Seeing as she was mistreated in the past, that may be easier said then done. Is she hand fed at all? Hand feeding can make a LOT of horses super pushy and nippy. What I do with my mare is not give her a treat until she moves her head and looks away from me. She knows when I have a treat and she'll whip her nose around to get it, then realize she won't get it that way and corrects herself, looking straight ahead and eyeballing that treat like she's starving, then I'll give it to her. The trick is just giving the treat to them on your own terms, not letting them take it from you. Biting is a bad habit, and you don't want her to start it [obviously.] If she looks like she is going to bite you or someone, a really sharp "AH!" sound can distract them, but you need to do it before she bites. Depending on her past experiences, it might not be okay to do this, but I ALWAYS bop horses in the nose if they try and bite. It's just something I will not tolerate. Do you have a small round pen or pasture? You can free lunge her. Using your body language, push her away from you and keep her going at at least a trot until she submits. That is, lowered head, licking and chewing, keeping her inside ear on you, etc. It's a very natural process in the horse world, and it will prove your dominance. Some horses catch on quick, others not so quick, so you could keep her at a walk/trot since she's young. You don't want her to over-do it. I hope something I said ends up helping =]