I would take her to the vet!!
It could be something other than fleas.
Fleas cause severe itching, and you can sometimes see them on the coat. use a comb and comb around the neck and base of the tail. apply what is removed to a wet tisue. If you see any red specs you can be sure there are fleas there.
Personally i use Effipro which is cheaper than Frontline and i've had no problems with it. I think flea treatment has to be changed every now and then to prevent immunity to the drug used.