She sounds really locked up.
What I would do is find a dressage whip or something. Put her hindquarter to a fence, and holding her steady with one hand, use the dressage whip combined with pressure on the halter to encourage her to sidepass away from you. It will probably be ugly for a while, and she might get upset. The key is to stop when she's moving off the pressure correctly, and to not give up until you get the desired result.
Once she's comfortable with the sidepassing, take her back away from the fence and start asking her to plant her hind foot and start her pivot.
It probably won't happen in a day. Once you've made it to a positive stopping place (crossing over, or moving away from pressure well, etc.) pet her and stop for the day.