I would assume your daughter is lying to cover her butt and safe face with you, her parents, and assume that all of the girls participated equally in the night's poor choices and discipline her accordingly.
The thing is in my house (I have a 17 year old daughter and 16 year old son) it wouldn't matter if my kids were perfect angels that night if they were there, and they didn't leave the scene once things started to go wrong, they would be considered just as culpable as if they actively participated. In my house, there is no difference. You don't get any points for saying "I just watched my friends get high and start sexting, really I didn't do anything." Um...no.
When my son lied about sleeping at a friend's house and was really in a house with no parents, his girlfriend, and another couple for the night last spring, I grounded him for 6 months. From May - November he had no phone, computer, iPad, and wasn't allowed to have friends over or go anywhere. All summer he pretty much worked, baby-sat for me, did chores, and played guitar at home. Oh and he also had to attend counseling sessions.
Your husband is having a knee-jerk reaction. I think his restrictions right now are fine and appropriate, but they need to have an end date and switching schools is pretty drastic. Figure out how long the restrictions really need to be in place for them to really stick for her...a month? Three? Six? Six months earned me the "crazy mom" reputation among my son's friends but you know what? He doesn't mess with me anymore, and his friends know that we he say "no way I'm not doing that remember what happened last time" they know it's no joke.
Finally...now you know that this was an incredibly stupid thing for you to agree to, right? And you now know that you will never, ever allow one of your children to spend the night unsupervised at someone's house? Honestly you're lucky that something worse didn't happen and that they didn't invite boys over, etc. Live and learn.
It's a sucky thing to go through, but if this is the worst crisis of your child's teen years, you're pretty lucky. I was beyond enraged and upset last spring but we laid out the punishment, he took it, and it's over. You have to be able to forgive her and move on. And when she starts to earn back your trust, your rule has to be trust, but verify. And no overnights without parents, ever.