I don't know, and you don't either

Yes, she was acting crazy. Yes, she did some awful things. But do people not get that she was basically having a nervous breakdown? People deal with grief in an infinite number of ways, many of which make no sense. Not only is Franky grieving for Grace, she feels responsible for Grace’s death. I think in this ep everything sort of hit her all at once, and she acted out. She did things that she wouldn’t normally do. Sometimes when everything feels so fucked up, the only solution seems to be to change everything in your life, because you feel like things can’t possibly get any worse. I wouldn’t be surprised if she did a lot of it in a daze/without being aware of what she was doing (see the scene where Luke is beating the shit out of Nick: there’s a moment where it’s like she’s snapping out of something and wondering how the hell she got there). Between the drugs, the alcohol and the adrenaline, it’s no wonder she just kept getting worse. And then, when she realized it had all gone horribly wrong, she didn’t know how to get back on track.

Say what you will about Skins - specifically its writing - but I think this ep was a pretty brilliant character study.