E.C.
hmm...chances are the problem will *eventually* be addressed when they start hearing their child repeating those words - nothing like the surprise of hearing a little voice saying @#!% to make parents more careful about what they say around kids
seriously, though, if you don't want to wait that long, is your friend the type of person to whom you could just gently say that you've heard other parents tell of how much language-good and bad- that their kids pick up from them and so you've been trying hard to cut down on using those words around your child? it *can* be a difficult habit to break (maybe she's trying but just slips up a lot?), in our house my husband and I try to make a little game of it by just thinking of some silly word when we catch ourselves mid-swear ("um, 'shish-kebabs,' yeah, that's what I meant, we ought to grill some for dinner")
and when the day comes that your kid utters a word that's, um, not appropriate, a great book to share with him is "Elbert's Bad Word" by Audrey Wood - it's a humorous tale (with hilarious illustrations) of a boy who 'catches a bad word' (illustrated as a fuzzy bug-like creature) that he overhears at a grown-ups party. He unintentionally utters the word when a heavy object falls on his big toe and chaos ensues, fortunately he learns how to express himself more appropriately....actually, it might be a good book to share with your friend now, as it shows (in a comically exaggerated way) how our word choices can have unintended consequences.