I honestly love groundwork. It's so beneficial. I would get her working on yielding to pressure. It will make her softer all around. I think you should restart things very simply and gently. Through getting her to do things by choice and not forcing then she will be obedient and more willing. I would start with just a halter, a whip(dressage preferably for the future), a lunge whip and a lunge line.
Work on: 1) Getting her to lead well at the walk and trot. When you stop she stops, when you turn she turns. She does not barge ahead of you or lag behind you. Aaaaaah I'm so tired, I'll give you the best exercise I can give with my half awake mind:
I don't know where she is at on her groundwork training so I'll start simply.
Lunge her around you at the walk on a small circle. You should be in the "lunging triangle". In my opinion, there should be slack in the rope and only tightened to slow her down. My horse is so in tuned to my body language that I stop him with...my body language. I'm too tired to explain, I can go on about body language for hours. So just get her to lunge both ways at the walk, slacked rope, get her forward. Do walk-halt transitions and turn her around. Once she is stretching her head lower then ask for a trot. Do walk-trot-8 steps-walk. This is not how you have to always lunge her, you are getting her in tuned to you. Repeat that both ways(now on a larger circle because she is trotting). Between the trot transitions, allow her to relax at the walk. Your goal is to have her relaxed, with her head low(not in frame) at the walk and trot. Relaxed doesn't mean slow. She needs impulsion. Goal: relaxed at walk and trot, responsive to cues and doing transitions.
Exercise numero two: Yield to pressure from halter(if she doesn't know lunging, then this is still a good exercise)
Grab the side of her halter. Stand to one side beside her shoulder. Gently pull on the halter, mainly sideways but a little bit down. the second she moves her head the direction you are pulling her(kind of to her shoulder), release immediately. This simple exercise will help teach her to respond to pressure by anticipating a release. Pull, release. If she pulls against you in an upwards direction, do not release, but do not pull more. Just continue up there. You must make sure that even if she only gives a little tiny tiny bit, you release or else her throwing her head in the air will be your fault. This is not meant to be a pulling battle. If she releases cm by cm then so be it, she will get it. Do it both ways and also downwards(in this case the bottom of the halter). Make sure you ask for slightly forward and down because if you ask for backwards in down she will move her head to far back(behind the vertical). You want her reaching down like she is grazing. This will actually make her calmer.
Try something with her too, I just want to try to understand her more. Put your hand behind her ears with your four fingers on one side of her crest(top of neck) and thumb on the other side. Push down hard, tell me if she gives to that pressure. My horse is an absolute fighter and just pushes back, he's much better now. This will be a good exercise in the future but I need to know what her reaction is. If she puts her head lower, that is very good. I don't want it to be a fight for submission but an exercise that can help relax her. If she fights it, then working on pressure and release will help in the future. A willing horse that trusts you will drop its head.