Is this fair? Or is she wrong?

Okay so I have a group of friends. There are ten of us, but some of us are closer than the others. Samantha is my closest friend inside of our group along with Liam, and Iven is Liam's closest friend. Liam and Sammy like each other and Liam recently took her virginity and has with her casually, but he has a lot going on with him at home. His dad is an alcoholic and he's currently going through therapy for trying to commit suicide, and for a cocaine addicition. He uses these things as reasons to not commit with her. (he's also sort of a player) Now, Sammy feels dumb for giving herself to him like that so many time so she retaliated by sleeping with Iven. (Iven is a player and he never turns down.) Iven called me after wards and told me what happened, and I'm kind of pissed at Sammy because she knows how Liam feels about her, what he's going through, and she knows that Liam trusts Iven like a brother. I think she was selfish and manipulative and when Liam finds out he is going to feel very betrayed. He already has a lot to handle. Do you think what she did was wrong? Or was it okay since Liam still hooks up with other girls and isn't actually her boyfriend?