NixNox....I am wondering, on top of everything...does she have any preexisting impulse control issues...like ADD/ADHD? If so, and it is not addressed, it thickens the pot, considerably....
With her history, she really needs the help of professional mental health persons....you can be her parents (also, with professional support)...but, you can't be her therapist....
Remember.that you do have considerable leverage, as she is living in the family home and largely at the family expense.....
You and your husband really do have to be a tight team...as these kids can be masterful at manipulating and "splitting" the parents....
I am wondering if you have been the lead parent....and, not your husband...? Just asking. Because he is the biological parent...and, unless he is some sort of dysfunctional mess himself, he would be the most logical parent to do the leading. The biological parent almost always has more importance than the step parent...even though you may have done a lot of the work....(step parents always are in a less than favorable position)...biology is powerful and it counts a lot.....