The cheaper stuff at Petco your friend is talking about is cheaper brands like Hartz or Biospot, etc., not Advantage or Frontline. Buying Advantage or Frontline from Petco is just fine. It's the same stuff you get at your vet. The cheaper brands of flea treatments contain pesticides that can cause seizures, skin problems, hair loss, etc. and these should never be used. Of course your cat could have a reaction to Advantage or Frontline too, like any medication or product you use on them, but they are generally safe and effective. I use Frontline on my foster cats that come with fleas and it works great. All the little suckers are usually dead in 24-48 hours. If the infestation is bad and the kitty is itching a lot you can also give her some Capstar along with the other stuff. Capstar kills adult fleas in about 30 minutes but it only works for 24 hours while the other stuff works for 30 days.
I don't treat my home for fleas but I do make sure to vacuum well and wash anything that can be washed to get the fleas out of the environment. If you treat your cat for 2-3 months with Frontline or Advantage (or Revolution which has to be bought at your vet) any larva or fleas in the environment will have gone through the lifecycle and will die out on their own. So in my experience treating the environment beyond cleaning and washing is usually not necessary unless you have a really bad infestation which you probably don't.
If your cat has fleas chances are good that she will have tapeworm too. They get tapeworm from ingesting fleas. You usually don't see any signs of it until after they've had it for a while if you see anything at all. So to be on the safe side I would treat her for that too. You can get some Profender from your vet which will also work on other worms in case she may have that. You can get tapeworm pills too but they can be a pain to get into the cat.
Does your cat go outside? If so you really should keep her on a flea preventative monthly at least during the warmer months or year round (ask your vet). If she goes outside she should also be dewormed twice a year unless she's on Revolution which prevents/treats worms.
