Losing my Mind with Teens

Kids are great, until they hit puberty. Then it all goes downhill. I've got a wonderfully moody teenage girl here, one who thinks she's everyone's mother (and I do mean everyone's), who's also a slob and won't take responsibility for her own actions.

I've been trying to get her to stop trying to be mom to Joe, Steven and Beth. It's definitely not her place, and it's way more than annoying to have her yelling at Beth to stop doing something (or to do something) when I'm right there...either getting after the girl myself, or allowing her to do whatever it is she's doing. I mean really?? If I approve or am already disciplining, why the hell do I need a 13 year old doing my job? And I can't break her of the damn habit either. Not sure what to do to get this behavior to stop.

And not really sure what to do about her stuff. The girl is a friggin' slob, and I had her clean her room spotless before Beth moved in there. Also told her that she needed to put everything up and out of Beth's reach unless she wanted Beth in it...because we all know toddlers get into absolutely everything they can get their chubby little hands on. Now, every time Beth gets into something in their room, Faith goes nuts yelling at the child. Doesn't matter that it wasn't put up in the first place, just that Beth got into it. Not only that, but she blames Beth for every single mess that's in that room, whether it was actually Beth or not.

Today, we ran into both these issues plus one. She tried to kick Beth away from her... literally kick her. Of course, I'm yelling at Faith already because I'm tired of the blame game, and go ballistic on her when I see that leg kicked out towards her little sister. Seriously?? What is the friggin' point I'd like to know? Not only that, but Faith doesn't know when to shut her mouth and just curse me under her breath (like all teens do). Nope. Instead, I get to hear her try to "explain" her way out of all this shit (excuse the language). To make matters worse, even after I tell her that I don't want to hear any explanations, I know the issues at hand, her explaining is only making matters worse, she continues to try to explain. Which makes me even more mad. Know what started all this today? She wanted to spend the night at a friends house because she's been grounded for 2 weeks and hasn't been allowed to stay over anywhere during that time. I told her no, because her room was a mess. Instead of cleaning it up and asking again, she digs herself in deeper. That, I just don't understand.

Anyone have any suggestions on how to handle this situation? I know I can't be the only one that's dealt with this before...and I pity those who've done it before me. Sad thing is, I've done this before and had no way to deal with it because the girl wasn't mine and her dad would reprimand me for disciplining his daughter. We don't like those folks now, and I'm tempted to tell Faith that she's acting just like that girl, but I know that's just counter-productive.