Sounds like she is really nervous of you being around the back of her. I'd say just keep working with her, and as she gets more quiet and calm she will stop the behaviour. Brush and touch her a lot around the hindquarter, rub down her hindlegs, her udder, her tail, etc so she is used to it. Good luck!
Agreed, She needs lots of non threatening TLC in that area. alot of visitors will also help.
Rub/scratch/brush/lean on etc.... we have often scatched under the tail and on the inside of the back legs. at one point we had a heifer that would twist her rear in the direction she wanted you to rub brush or scratched. This heifer may have been hit pretty hard by something, someone or some animal ( a few times) on her southbound end.