Cats flea advice

My sisters cat has fleas xDDDDD

Ok she rang vets and the appointment times they can give her, she cant make any of them, because of work. And the vet wont give the treatment out without checking the cat first.

So is there any other good recomended flea treatment that is available? Something i can buy off the shelf.

How often should a cat get flea treatment? do they need regular needles in them?

EDIT: oops problem solved, Vets said they can keep the cat till th evening.