I have the same situation with my ex - only add to it a tv that never gets turne off - my son usually watches 3 or 4 movies every weekend he's at his dads, plus plays video games nonstop. I've asked him several different times if he goes outside or even goes anywhere and the answer is either no, or "yeah, we went out to get chips and movies and buy video games."
Fortunately, he spends most of the year with us and is a very compliant child (I'm assuming the stepdaughter you only see on weekends or such...) He knows the rules are different here than at his dad's and that he has to be obedient. He also sees the fallacies in his dad's lifestyle, altho we've not pointed them out. We have had, however, issues in the past with "Well daddy lets me do this" or mouthing off to us the way his dad does or trying to play us against his dad, which never works and just results in infinite amounts of trouble for Joey....
Be Clear on what the rules and consequences are - we have them posted in the kitchen.
Be Consistent with discipline - every time. It's hard but it works.
And I highly recommend your husband being the one to enforce discipline with the stepdaughter otherwise it could get ugly in court. Also, If her dad doesn't care, there's no way you're gonna make her care. I would definitely agree that a tete-a-tete etween the father and daughter is in order in which he outlines the rules and corresponding discipline, showing it to her in writing, ensuring that she understands, and him demanding obedience and respect for the individuals in your family, your family unit, and the house. Then, if she CHOOSES to break a rule, she has done so fully knowing the consequences.
Good luck!