You kill the flea! Doesn't matter how, just kill it. I usually drop fleas - and ticks - in the commode after I've killed them to make sure they're really gone, lol.
As long as she bathes him inside and keeps him in a warm room until he's dry there's nothing wrong with a winter bath. I'd suggest a flea shampoo with Neem as the active ingredient. It's an organic insecticide that is non-toxic to man and beast. It's the only active flea ingredient I've ever been able to use on my dogs without having my hands and arms itch for days afterward, so I can only imagine how much better it feels on the dogs' skin. Most good pet supply stores carry it, or you can probably find it at a health food store that carries pet stuff.
Many dogs are allergic to regular flea collars, and I've never found them to be terribly effective. There are organic ones available, but I haven't used them, so I can't tell you anything about how effective they are.
I've never had much luck with the garlic and brewers yeast added to the diet either, and it tends to make some dogs pretty gassy.
I live in an area of the country that's very conducive to fleas and the only thing I've ever found to really keep them at bay is the stuff you get at the vet's that you put on the back of their neck. I don't use them at all during the winter months though. Every now and then I'll see one or two fleas, but I figure the dogs are better off with a break from the flea meds for a few months. During the cold winter it's pretty easy to keep fleas at bay with an occasional Neem shampoo.
I DON'T like the idea of the pills/treats that are supposed to keep them flea free. There's no way something like that can be good for your dog's health! My vet doesn't even offer them as an option.