What to do...?

I knew this time would come, but now it is here I don't know how to handle it.

13 year old Rose has hit puberty and has started battling with her mother (as we all did). Both of them are strong personalities with very low tolerance levels and extremely short-tempers so the battles are often and nastily fought. Rose speaks to her mother (the Banshee) as she is spoken to and her mother doesn't cope well will this. The Banshee seems to think that the winner of the argument is the one who comes up with the most hurtful comment, and the Banshee hates to lose.

So... she came to stay with us for a week. She did well to last that long with the Banshee calling every night to ask when she would be home, and her older brother conscripted to continue the guilt trip at school. She has gone back now but I think she has achieved some of what she wanted. Both she and the Banshee now know that she is stronger than her brothers and that if it gets too bad at home she will come to us. The power balance has shifted a little, which I suspect will only escalate the battle.

I know I sound cynical but I was a teenage girl once and lots of split families I know deal with these same issues. DH thinks that he is offering a 'safe haven' for the kids to come to because their home life is so difficult, but it is also a great tool for a teenage girl to get her way. The whole time she was here she was on the internet finding horses for her father to buy her, because "I would definitely live here all the time if I had a horse".

Naturally DH wants to buy the horse. Naturally I am not so sure.

The relationship between mother and daughter is a curious one - the ties are deceptively strong. Not to mention the force that is mother guilt. What happens to DH when she chooses her mother over the horse (and him)? What happens to DH and I if she does come here to live and starts battling with me?