I have a four week old puppy she has fleas, was told seven dust works if you put it on them - does it?

I don't know about 7-dust but there is a product called tea tree oil, it can be used on cats or dogs. Takes care of fleas and any wounds resulting from fleas. Uses once a day until wounds are gone if any. Or until there are no sign of fleas. Then continue once a month to keep pet flea free. It's messy but worth it! I have used it for my cats and it works wonderfully. Hope this helps.