Its really sticky whether you want to talk to her husband directly about it or not. 
But if it was me, I would talk to her husband directly and talk about it...because I care about her and dont want her to catch diseases from her husband that he could've gotten diseases from some guy. You know, if I decide not to talk to her hubby or tell my friend about it -- then later, your friend end up got bad diease like AIDS? I would feel guilty about it and wish that I should've talked or tell my friend about it so it wouldn't never happen to friend to get AIDS that she didnt deserve to get it from her husband? You know what Im saying? Its up to you. Good luck.
