If I were the friend, I would rather stick with her than joining other bands. Friendship is more important to me.
But maybe I can only say that because I don't really have any hobbies I'm passionate about.
Edit: now that I think about it, the friend knew she could play guitar. Shouldn't she specifically find a bassist instead? It was inefficient for her to invite a random without knowing what they play.
That bitch is awful though.