I used to ride a horse like that. Eventually, I gave up on arena work altogether. It just wasn't worth it of me to have to 'push' my horse so much.
My trainer at the time said the problem is that I WAS pushing. Horses hate to be pushed, and they will often push back against that.
'Pushing' can be a lot of different things. It can be your squeezying too much with your leg, on their flank. It can be repeatedly nagging, It can be putting leg on and pulling back with the rein at the same time, it can be trying to move them somewhere when mentally they are wanting to go somewhere else, (so trying to make them move their legs when their mind is not ON you and your request.)
When my trainer would ride, she would use very little leg at all, certainly never a hard leg against their side, and never more than one or two light taps, if any. She would focus on a point on the other side of the arena, and raise her own energy , in her body, which is a very perceiveable cue to the horse, and if the horse did not respond, she would take the long ends of the reins and slap them back and forth over the shoulders.
The point is not to reinforce your leg , as the so-called 'tapping' of a whip behind your leg, but rather to wake up the horse, gain their attention, and say, "hey! I just asked you something. pay attention!"
Once they react to that, they will usually leap forward a bit, startled, yes. Your job is to accept that forward, and not to try and mold or keep it in any way for a bit. The idea is to get the horse to realize that he has freedom in moving forward. of course, eventually, in dressage, you have to 'mold' that energy by asking for bend, or for collection or extension or a stop or a change of gait. But, when the horse gets dull or resentful, you go back to just getting a forward, and rewarding that.
I know you said that she will do this, but one thought is if you can get a forward from the cue of raising your energy in the seat (which you reinforce with neck slap if she ignores you), she may become less resistant to any leg cue asking for bend, for instance.
The idea is to build her sensitivity to your seat and your energy and your leg, by not overusing your leg.
I'll close this by saying that I invariably would start out with this concept, in my rare arena riding times, but would devolve back into pushing, pushing, pushing and becoming resentful at my horse's resentment and holding back. I ended up going back to the trail, where we both had more fun!