Hi Martha! Welcome to Ask Amy!

First let me give you the deeper answer. The truth is, the healthier the animal, the less likely they will get fleas. I experienced this with my dogs.

My first dog was in my pre-homeopathy days. We did all the vaccines, flea collars, normal dog food, and all the rest. She died from cancer at age 10.

My second dog was in my homeopathy days. Although we got her from the pound and she got some vaccines and a flea bath there (she was 10 months), we avoided vaccination from that point on (for most of her life, just a 3-year rabies vaccine, and nothing at all in her elder years), fed her the best natural dog food, she was under the care of a homeopathic vet the whole time getting her constitutional remedy, and in her later years we even fed her the BARF (bones and raw food) diet. She lived to be 16 and was a largish dog too! She basically died of old age. And…
SHE NEVER HAD FLEAS.. We never used a flea collar. I know this for sure, because I am really reactive to flea bites. If I even pet someone else’s dog, even if they use flea collars and don’t think their dog has fleas, I often get a flea bite from them.

So the long answer is — find a homeopathic vet (most of them in the USA are licensed vets) — follow their advice, and your pet will likely no longer have fleas anymore. To find a good homeopathic vet, try: The Academy of Veterinary Homeopathy
http://theavh.org/
Many of these vets have been trained by Dr. Pitcairn, who is really considered the “father” of homeopathic veterinary medicine, at least in the USA.

The short answer is: there is not “one remedy” for fleas. I don’t think so anyway. I recommend you consult the following two homeopathic veterinary books:

Homeopathic Care for Cats and Dogs by Don Hamilton
Dr. Pitcairn’s Guide to Natural Health for Dogs and Cats by Richard Pitcairn

These books will likely provide some specific remedy guidance for this specific problem, as well as others.  So buying one of them will probably be a good investment!

However, one remedy that does spring to mind, is Staphysagria, which is often a good general remedy for dealing with parasites.  For example, it is useful for a child with lice. Notice, once again, that it is more about treating the tendency to become vulnerable to parasites, rather than about treating the itching itself (with a remedy like Sulphur).

I hope this is helpful! I wish I could give you a simpler answer, but as is often the case, the truest answer is that a remedy that matches the patient is the best defense against disease, and in this case, susceptibility to parasites.

-Amy