Thank you so much!! Will definitely give it a go! :)))
Don't let her push you around if she's trying to run through you to get to the filly. A firm "hey" and a yank on the lead rope should suffice unless it gets dangerous. Then I would suggest finding an area away from the filly where she can eat hay, be feed treats, and get groomed. This will create a relaxing atmosphere away from the filly. Then after she relaxes a little she will more than likely get worked up again. When she does that take her to the field the filly is in or next to the filly and do a strenuous lunge session. Take her back to where you had her before (out of sight of the filly) and do what you would normally do, but make it extra loveing and add a few treats in. It would be best if she could not be turned out next to the filly as she will just have more time to make a bond. Essentially, after quite a few sessions (maybe less depending on how bad it is) she will associate the filly with work and everywhere else as a more pleasant environment, and will get over her anxiety! Hope this helped!