[genrex]

I had that issue with my step-daughter as soon as she graduated from high school. We had mutually-agreed house rules but they were not obeyed (no overnight guests of the opposite sex, home by midnight, if not home by midnight, then she was to call to let us know where she was, which she always "forgot" to do but it hardly mattered because she wasn't doing what she said she was doing). There was no punishment for breaking the house rules because her mother wouldn't allow any punishment of any kind. Lots of acrimony in the house.

We got her a nice one-bedroom apartment at a secure apartment building, and we furnished it with her stuff and some of our stuff. We paid her rent and utilities. She paid for everything else with her part-time job, and she did her laundry at her apt building. It kept the peace in the family until she went away to college, and it was a huge relief though it was a financial burden. I saw the inside of her apt only one time during that year, and it was filthy, but nothing was damaged. She was socially and sexually active, but was smart and didn't get pregnant. Then when she went to college, she lived in a dorm on campus and then an academic sorority house. Graduated with honors and has a nice job in Chicago. It worked out for us.. *sigh of relief*

edit: Your step-daughter is still in high school. But she is 18. I don't know what I would do. Somehow the stress has to be relieved..