Honestly, I agree with all the PP who've said that the only thing I would have learned from this as a 14 year old is that my parents don't trust me, and next time I should just lie and say I was staying over a female friends.
You know that there are a number of her peers there, so
a) either those parents have let their children go - so what, does that mean they don't love their children as much, or that there is something about your child that makes her more vulnerable?
b) or - the other teenagers have lied to their parents, and been rewarded by a fun night, whereas yours has tried to be honest with you and been punished by missing out. Is that the lesson you want her to learn for the next 4 years?
If she was going to have sex, drink, or do drugs she could do them as easily in a playing field at midday, or after school, or in a cinema, as she could round a friend's house on a weekend night.
At least if you'd shown her you trusted her and made arrangements to pick her up at 10pm you'd know where she was and had limited the time period she had to get into any trouble, plus kept the lines of communication open just in case anything did happen that she wasn't comfortable with.
I don't think teenagers should do everything they want to btw - I'd agree that a sleepover might be inappropriate, but hanging round someone's house for a few hours of an evening is pretty tame as far as teenage activities go.