You can't believe under your roof that she would act like such a whore! Well since your step-daughter wants to act like a whore you might as well treat her like one. You write out a contract, conditions for her to stay living under your roof. Its simple really, obey the rules outlined in the contract or pack your bags and leave immediately. Thinking its a sick joke she signs it, not realizing just how serious you are. Now her fate is sealed, weather she likes it or not she is your new personal free use fuck doll. Apprehensive at first, she comes to love the taboo nature of this new contract, eventually begging you to fulfill it.