This subject is so interesting to me. My dd has had 3 different girls over the last few years spend the night at our house and I never met the parents until after the fact. It is unbelievable to me that someone would drop their kid off in the driveway and never come in to meet me.
That for me = friends dd will NOT be spending the night with. If they don't monitor their kids I know they won't monitor mine.
My dd or ds will NOT be spending the night with someone I don't know. And in my opinion if the parents can't understand that then that just helps me feel like I am making the right decision. I want my kids to be around families that have the same values and ideas as us when it comes to raising kids...that is what will make me feel at ease about my child being at their house.
I also think meeting someone for 5 minutes when you drop your kid off is not knowing someone enough to leave your kid overnight at their house.
This has happened to me. DD invited a friend to a party, and the parents just...dropped her off; by the time we got to the door to let her in they were driving away. They didn't even stick around to make sure she got in the house!

Now, it's been over a year, and this girl has spent the night with DD several times, and I have NEVER LAID EYES on either of her parents. Sometimes we pick her up. I go to the door, hoping to talk to a parent, but the girl comes out alone. It boggles my mind. DD will NOT be going to her house, but then again, she's never been invited. I don't think they want to be bothered with thier own kid, much less anyone else's.
On the other hand, I have had a girl come to a sleepover who had recently moved here and her Mom called and chatted with me awhile. She was so happy that her DD was invited as she was worried she wouldn't make new friends here, but she was also concerned because she didn't know us. I just told the mom, "Well, let me just tell you all the things you would like to know but feel too awkward to ask. We are Christians. We don't drink. We don't smoke. They are going to watch a movie and it will be Rated G. We have a Wii, but the games are rated E (we have Mario Kart, and Mario Party, and the sports package that comes with it). We have no accessible guns. DH has a rifle that was his grandfather's but it's in a locked gun safe in the attic, unloaded, with a trigger lock. We have 4 cats inside. My husband and I will both be here. We don't allow them to listen to music with foul lyrics. They will have to be in bed by 12:30-1:00." I think I even told her what we were serving for dinner, late night snack, and breakfast, too. By the end of it, we were both laughing and she felt very comfortable with her DD coming. She admitted she was concerned about guns and was okay with it being there since I told her just how inaccessible it is (we've lived in this house 12 years. NO ONE but DH has ever been in the attic. It has those pull-down stairs, and the girls and I are scared of them - lol. Every year, he offers to let them go up with him to help get the Christmas decorations down, and they get halfway up the ladder and chicken out. There's no way they'd get up there without us knowing - those stairs are LOUD when you pull them down. The gun safe has TWO combination locks, and *I* don't even know the combinations. I feel very confident that there's no way anyone could get to this gun. DH only keeps it for sentimental reasons, because his grandfather gave it to him). She also appreciated knowing about the cats, but said they have cats too, so no problem. DD does have a friend with cat allergies, and when she comes, we put the cats up and vacuum REALLY well.
I think this party has already started, so the OP has likely made a decision by now, but for next time, RSVP sooner and see if you can meet the mom for lunch someplace beforehand. Also, even DD13 has had friends who "can't stay" and they don't need a reason. Some have early morning sports stuff on Saturdays and the parents know, despite my best efforts, they won't get a good night's sleep. Others I think just don't want to sleep away from home yet. You don't need a reason - not for the party host or your DD; just say, "Thank you for inviting DD; she can come on Friday, but we'll have to pick her up around 11:00 because of a previous committment." No one but you has to know the "previous committment" is one you made to yourself not to let your DD sleep away with people you don't know well.
But do try to get to know the family; if their DD likes yours well enough to make her "A" friend list (if she was only allowed to invited 2 friends, and she chose your DD as one of them, that's pretty significant) then my guess is your DD will be invited to other things in the future.
