Wow....that ones a toughie. I feel for you.
What I personally think is your step daughter is a little spoiled. I think the best thing for her is a big fat NO. It really sucks, but it will help her in the end.
I wouldn't go to her directly, because it will cause controversy. I'd go to your husband, tell him your opinion, and leave him to his decision. I'd make sure you make him see what you see. Sometimes parents can be blind to that.
I hope it all works out for you. Let us know how it goes.
Desirae