I agree 100% with what the others here have said. If she did that when you touched her back, there is most likely something wrong with her and it's painful.
She needs to be seen by a vet asap.
If you can't afford to take her to see a vet today, I suggest taking her back to the rescue where she can get the medical attention that she so Desperately needs.
It would be horrible to see her attack someone more severely than previous episodes because her pain had gotten worse.