There has to be more behind it. Maybe she had been acting up all weekend and this was the end result. Maybe he feels like she was giving him the finger by knowing his rules, sneaking behind his back, and hiding the soda's. She may have lied about it. I would try to listen to his side of it. I would also explain to her that even though you may not agree with his rules, he's still her father and that she needs to respect what he says the same as you would expect it in your house. I also think you need to send her, as hard as that will be, because if not, you are pretty much taking his authority and respect away. Then, after this weekend, talk with him about her getting older and maybe needing more space (less time) with him, or allowing her a little more say in when she comes and goes (since he cancels all the time, it shouldn't be a problem). I think if her step father had wanted to discipline her, you'd step back and let him parent, and you really need to let her bio-dad have the same/similar respect. Btw, he'll probably be cooled down a bit by the weekend and won't be so mad anymore. It may open some line of relationship that they haven't had before, or not, but she needs to see you wont lie for her or "save" her from punishment. That's my thought, good luck, it will pretty much suck sending her, I know.