I have had two horses that have had that same issue. The more pressure you put on them, the slower they went, the more upset they got, one would buck, the other rears. You do need a certain amount of contact when riding, but a lot of the forward movement should come not from your legs, but from your seat. Contact to me is just having my leg on enough that it gives me good balance, keeps me in the center of my horse, and keeps my leg from swinging as the horse moves. I was incorrectly taught to keep my lower leg on at all times, and therefore was pinching my knees for years until I went to a different trainer who has helped me retrain my body to ride the right way. The horse I have that has stopped having issues with my legs, I spent a lot of time just asking for movement, as long as it wasn't backwards, or up in the air ect., and when he would move forward, and I could put my leg on just a bit, I would praise him a lot, and let him stop, and after a while, he now has no issues with my leg, as long as I'm not trying to squeeze with my lower leg, or kicking him. Lots of baby steps, give and take, and praise to get her to where she's not dangerous when you have your leg on.