Even with the situation with Lee, she seems to have understood (and expressed to his face) that he seems to have been leading Casey on. You could tell in that instant that Jasmine had been assuming he'd been a decent guy about it and parted with Casey fairly, and suddenly realized he wasn't and didn't.
That said, remember she's also known for sleeping with a married man, Mr. Arquette. So she might be extra sensitive about that one area, after all the "marriage wrecker" flack she got, even though for the most part she's "do whatever the f@ck you want".
And of course she did an about face later on when others were in the room. I'd been hoping she'd stick it to Lee more after that, but she backed off and defended Lee to the others. Very disappointed by that.