Well, this may be part of the problem; she does know quite a few HG+ adult women... and most of them are loners who have finally given up on 'normal' social interactions.
Well you should all gang up and be "freaks" together!
(Or are these all just family members you're referring to?)
Your story about your first husband makes me very sad. I've gotten a similar reaction from people before, but thankfully no one particularly close to me, and my husband is as much of a freak as I am (if not more).
We do, though, have friends. But we've always lived in or very near large cities, so there's just more to choose from. My DH even had (by chance, it seems) a nice cohort of HG+ friends throughout his school years, and went to "nerd camp" where he met some people he still keeps in touch with. We both received full-ride academic scholarships so those came with a peer group that included some people who were smarter than we are. Unfortunately, due to moving around a few times, we don't have the awesome group of alum friends ljoy mentions.
If you're not finding what she needs with what you're doing now, cast a wider net. If going to a camp or retreat isn't viable for your DD, then maybe... set up a chat room for PG youth? You could advertise it here and on the Davidson FB page, and send it to all the summer talent search programs or PG camps you can find. Surely there are others her age in the same boat, it's just a matter of finding them.