Re: Is her husband cheating?
Did your friend wed her husband in a civil/registration ceremony (or whatever you call it there)? That’s important for her to figure out what her rights are.
If he did lie to her, remaining married to his first wife, he’s the worst sort of lowlife and quite frankly your friend deserves better than him. Before the guys jump on the “but multiple wives is allowed in Islam,” they should remember lying isn’t allowed in Islam and he’s possibly lied to her twice about something as major as having another wife and continuing that relationship.