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Has she always been like this, or is this new behavior?
Is she spayed?
The first thing I would recommend is having your vet do an xray to ensure nothing is broken. Many cats are very sensitive in this area and will not allow their owners (or anyone) to touch them there. Although this is new for her, it may be a problem that has been developing over time and just now is to the point where she doesn't want to be touched at all. We have a selkirk rex male who reacts the same way when touched in that area, and he has been evaluated many times by the vet (and by a veterinary college) with no problems found. There is a syndrome some cats suffer from called 'rolling skin disease' or feline hyperthesia syndrome. Here are links that discuss it more. Many vets feel this is a 'mini'seizure' disorder, but others feel that cats are in pain. Treatment IS available for the disorder, which you may want to discuss with your vet after other problems have been ruled out.
Please let me know if I can help you futher in any way!
The next time you take her into the vet, ask them to xray the area - just to make sure there isn't a break or problem with the tail or spine. Better to be safe than sorry.