If you've thoroughly checked her and there are no fleas present, she either has a flea allergy to the occasional bite (which chewing in those areas is a common symptom of), or a reaction to the flea spray (which is where my money would be on) .
Did she start chewing right AFTER this flea treatment, or has it been ongoing even beforehand? That would directly tell you whether is was the spray or not.
If she was chewing beforehand, considering those areas she is chewing at, those are classic flea allergy areas. It might mean that she gets the odd bite and is having a reaction to it.
Also, giving her so many baths, and the spray on top of it, may have really irritated her skin and dried it out. Sometimes they get inflamed skin, and the chewing makes it worse, then they chew more and it keeps going and going. It was good advice to get something from the vet to calm her skin, and stop the itching.