CURIOUS, my friend has a son with a dimple and I tried telling her that dimples are hereditary but only if the?

Anyhow I told her that dimples come only from the mother/father through the "Y" chromosome. She doesnt believe me but this guy she used to fool around with has a dimple so it like makes me curious if its this other guys son. I just dont know how to say it her and be direct. Its like GO ESTABLISH DNA!!!!!! You know, what would you do? would you tell her take her son for a dna test with this other guy, would you just stay out of it, would it really hurt her feelings, like I care as friend but I am thinking how it will affect her son its really all sort of screwy... what would you do