MomofC said no because she wants to see the movie first to make sure it's OK, and their weekend is too busy for other stuff. (As in, I said "what about if you see it Friday and we do this package on Saturday instead?" [it's available then too], she said they have other plans on Saturday.)
The thing that made this perfect is that sozlet just finally read the whole Harry Potter series and is absolutely obsessed with all things Harry Potter right now. C was in the exact same situation as sozlet -- able to read it but her parents didn't let her until she was old enough to read the whole thing, content-wise, since they knew she would tear through the whole series. (One thing I like about C is that she's another smarty-pants, and I think sozlet benefits from that, but C is a NICE smarty-pants instead of the volcano smarty-pants that is Esse.) (Volcano + pants a little unfortunate but I'll leave it.)
So, C and Sozlet have been talking Harry Potter all school year. They have like all of the major spells memorized and stuff. C is being Tonks for Halloween.
Since they are only just getting into this, they haven't been part of the whole Harry Potter hype up until now. They've both seen movies 1-6, but on DVD. Etc. (Actually sozlet hasn't seen 6 yet.)
A has been crazy for Harry Potter for as long as we've known her -- she's convinced she's Hermione.
Kay liked Harry Potter already but has been swept along in sozlet and C's new obsession (they do stuff at recess, etc., etc.) and while she hadn't read the books (but had seen movies 1-6) she is now reading them, and loving them. She's on 5 now and likely will finish the series by the time the movie comes out.
So, this is really Harry Potter-specific. But C is the obvious person to go, and she can't.
To add complication, I made it clear in the emails to parents that I was just doing preliminary feelers and wasn't sure what we'd end up doing, so shhh. But A's mom told her and A is SUPER DUPER EXCITED AND CAN'T WAIT.
Sozlet also complicated things by telling Kay about the possibility in earshot of others (she needs to remember that not everyone in the world has to see her to hear her). (She shouldn't have told Kay in the first place though. But I shouldn't have told sozlet if I expected her to not blab to her best friend. Argh.)
At any rate, right now, A, Kay and sozlet love the idea of going to the special showing.
The swarm of kids coming over for cake etc. might work. Every year I ponder whether I should start celebrating sozlet's half-birthday instead of her actual birthday as the weather is invariably miserable (cold and usually wet and drippy in a cold, near-freezing way) around her actual birthday. I'm not sure if the 25 or so in the house doing nothing in particular would work. Oh god. No, it really wouldn't work. (Just Esse is a terror, Esse + others on that list of 25 would wreak absolute havoc in about 30 seconds flat.)
Meanwhile, I plan to go back to see HP7 with captions, I offered to take C and sozlet to that (I'm sure sozlet would want to see it twice unless it's awful) at some point after MomofC has had a chance to see it. (Captions are usually about a week after opening, MomofC thinks that C and her dad will go on Sunday if the MomofC and DadofC viewing on Friday deems it acceptable.)
I'm puzzling over the keep the peace aspect. If she really doesn't want Esse at her party (Esse always seems to find a way to make drama and complication), should she give in because otherwise Esse will pitch a fit? Not sure.
(Definitely at the thinking-aloud phase, thanks all for sympathy and advice!)
Late-breaking thought -- forgo the VIP package and Leaky Cauldron and Harry Potter-themed games et al (it really does sound so cool though!) and take a group of girls to the movie AFTER opening weekend. I can still do HP-themed stuff at home.
And that still depends on C's parents giving the go-ahead after the movie, which they might not.