Wanky apologia
I'm guessing it's meant to subtextually tell us that Michelle really liked Peter, but she's bitchy to men she likes, and she thought that Peter understood and liked her and stuff when they slept together (and if they didn't actually have sex, then that could've coded itself in her head to "OMG he doesn't just want me for sex!") and then Peter called her the wrong name and didn't even REMEMBER sleeping with her and she was really hurt and angry hence superbitchiness + passive aggressive traps. Now, Peter seems to really actually want her when he's not drunk, so she can forgive his idiocy of the morning after as just drunk mistakes.
Unfortunately, this puts Michelle among the horde of women who unaccountably are over the top attracted to Peter who he dumps on. Because we all know whats going to happen when Peter comes back and Michelle insists they are in a RELATIONSHIP now.