Ummm yeah, it's "mwah". Did you ever hear Miss Piggy say "moy"? No. I've been to Montreal and I knew a French exchange student in high school. It's pronounced "mwah" and if your friend honestly thinks it's pronounced "moy", you need to tell her to just not bring up French again 'cause it's ignorance like that that gives Americans a bad name.

(Ignorance meaning, they don't know any better and don't care to find out the correct way. - I didn't mean that as a cut against your friend.)