How get ride of fleas on older cat nothing has worked?

I have tried Avantage several times, it worked great the first time but is useless now. I was bathing her monthly but my cat is 15 and it has become rather stressfull for both the cat and I (she bite me while trying to escape not to mention her claws are rather painfull ) I used borax on the carpets worked great but same thing ...not working as well now..keeps them to a minimum but never gets ride of them. I have put Apple cider vinager in her water..she wont drink it..same with the food. Skin so soft..leaves her greasy and she rubs it all over my furniture. She is covered and I am fitghting with the husband who wants to get ride of her because of this ongoing problem..It is to the point were we can not invite anyone over for fear they may have a visit from one of these critters. She's OLD, what can I do?