Is she bad?

My bestfriend has been with her man for a few years. They have grown extremely close and so in love with each other. Well...she is so attached to her man and her emotions are so wrapped up on him. Anyway as a couple of years ped by, she stated numerous times that they have been arguing more than when they first dated. When he is irritated, he treats her like she is the problem, etc...On Tuesday night, he called her and talked to her and said that they would talk again on Wednesday...it is now Friday nite and he has not called eversince. Well...she is close friends with a guy and when she went over to spend some time with her home boy, he KISSED HER and she became weak and ended up kissing him back. She told me that part of her felt bad and part of her felt good. I love her like a sista and she is a beautiful and kindhearted person, but does what she did make her a bad person? She made a mistake, so What should my friend do?