Yep, that's what started the whole thing. Her party theme was musicals. Her friends know every word to the soundtrack to the musical and it turns out she really was the only kid who hadn't seen it.
For the record, not one parent asked what we were doing or watching during the party. These girls were at my house for over 18 hours.
DD doesn't watch anything remotely scary like pp mentioned, no Stranger Things, can't think of any others, we don't watch much of anything. She isn't yet into much on the sexual front and still tells me when her friends do show her stuff that embarrasses her, asking for advice or just to get it off her chest. She's on the younger end for her grade, so some of her friends are older because of grade cutoffs and siblings (shifting so siblings wouldn't be in the same class) and with older siblings they are also exposed to more than DD. We don't have any alcohol in the house for them to get into, so that's not even on my radar, thanks!
We talked about it after everyone left. I wanted to make sure she didn't feel pressured into it, that she can always use me as the bad guy, and that she understood there could be consequences with the other friends parents. We talked about the other things those girls have introduced her to and felt that risk wasn't high. Other than that, she LOVED the movie, thought it was hysterical and thought Christian Slater had the coolest voice ever. We talked about R ratings and what to do if this happens to her with a movie she is uncomfortable with, or really any situation where she's being pressured into something that doesn't feel right.
Thanks for all your help and perspectives, I really really appreciate it!