If you keep her: Is there any where she can be put each day out of sight from the rest of her herd? Take her there for your daily sessions. Put new and different stuff around you so her mind is taken away from her herd. As soon as she gives you her attention, praise her and calmly lead her back to her herd. Do it several times a day so she learns as long as she is calm she gets to go back to her herd.
If she is ill mannered leading away take a long whip with you while you lead and insist on having her attention by pushing her rear away from you in turns on the forehand, backing up, going sideways, forewards, stop, back etc. don't give in to her manickness. If she acts rough by trying to lash out or kick, come down on her like a tonne of bricks and get rough back at her! Force her to pay attention to you otherwise she will get 'kicked' by your whip. Be dominating and a force to be reckoned with so she learns you do not tollerate bad manners.
As soon as she is listening, praise her. Make the right thing easy, the wrong thing hard.
Finding a trainer: Word of mouth is best. Go to your local tack store/ place where there are horsey people and ask for their opinions. Find a livery yard and ask the lasses there who they would reccommend. Get the name then go meet up with them and ask lots of questions along the lines of problem horses, youngsters, methods, success stories (too good to be true? Perhaps they're exaggerating to win you over??) and also ask if they've ever had any horses they couldn't train. Try them out and see how your filly reacts to them. If she shows signs of improvement, stick with them!
We lose ourselves in the things we love, we find ourselves there too ~Kristen Martz