She WILL push the envelope on EVERYTHING, just like a little kids pushes and grabs stuff until told "NO".

If she lived with her BF in high school you can be sure she is pretty much used to GETTING HER WAY, and if she can't do it nicely she WILL become both emotional about it (possibly even screaming) and could also engage in "punishing" you, ie: stealing, lying, making noise etc..

Girls are notoriously selfish at that age anyway ... girls who are used to getting their own way doubly so, and girls who are pretty too, well mathmatically cube the bad behavior of those three times over!!

FIXED RULES BEFORE SHE EVEN ARRIVES are a must, but with the provision that you CAN ADD TO THEM later. She may hate you for them, but initially YOU have the upper hand and can impose them. Over time if boundaries are set and she learns she has to follow them (don't let her get away with SQUAT that goes against the rules when she first arrives, you can loosen up later) you and her could actually grow to be quite close.

OH ... finally NO DRUGS IN THE HOUSE, even if YOU are currently using some. Drugs are BAD NEWS for kids that age and can result in her bringing very undesirable people into your residence as she brings her party friends home.

Good luck!!