WOW, things are going to get real crazy, real quick. At least you have some WARNING about difficult child behaviors... most people know the situation that our household is in, my step-daughter moving in with us because mom went to prison,,,,etc. Before we got her, she was in the foster care system, and the foster parent she was living with would tell the caseworker and ANYONE who asked that our difficult child was A PERFECT LITTLE ANGEL and that there were NEVER any problems....and when she came to visit, she was an absolutely polite little girl (she's 13 today, by the way).
So, when she moved in with us and we officially became the parents, we had NO IDEA what we were in for....and BOY did it hit us like a brick wall!!!!
Any teenaged girl, probably from about 12-15 are in that weird stage of life where they are trying to figure out who they really are and where they fit into the world even when everything is normal...add on being a difficult child and having to turn your life upside down and move into another house and learn to live with new people and everything, it makes for a very tough situation for her, and her difficult child'ness WILL show. I agree with the above, it would be a good idea to set down the house rules and consequences beforehand, you and your husband HAVE to be in agreeance and he must know that you and he have to stick together at all times or she will take advantage of you!!! Another thing I can suggest if you have any more weekend visits before the big move, go over the rules and the consequences beforehand that way there are no surprises, if there is ONE thing I have learned about parenting a difficult child, it is that they DON'T like things to come unexpectedly, they will always do better (not great, but better) if they KNOW what to expect.
I definitely would also make sure there is a treatment plan in place and a crisis intervention plan, both of which you should go over with her at the same time as you go over the rules, as these things may be PART of the consequences of inappropriate or violent/agressive behavior. If she's not currently in therapy, GET HER A COUNSELOR ASAP. Most of the mental health centers have 24-hour crisis intervention teams or on-call partners to help with the crisis intervention plan part, then you are dealing with people that KNOW your child, not random, unassociated crisis people who don't know anything about her when a situation arises.
Good luck, I know how stressful it can be to take on a step-child who is a difficult child, especially at that age...if you ever need to talk, I am here !!!!!!