The singing to Polly scene

I always get irritated with Susanna when she puts down the guitar and says "it's okay, come here" to the orderly because it doesn't seem like an impulsive act. It seems like she is acting on what she thinks she is supposed to do, or she is trying to impress Lisa. When she got caught with the other guy she seemed embarrassed, but now she has no problem doing whatever on the floor with this guy.

I figured that Susanna overexaggerated her problems with the promiscuity (and other things) so she could blame it on her diagnosis. And why was she telling people that she was crazy like that guy at the party when earlier she was freaking out that everyone else was crazy?