I'm enjoying this, but there's a serious continuity error here: you identify the time as 1975 in the first part: "I had no idea how to tell anyone that. This was 1975, and I had lived a life where anyone who wore women's clothes was a freak. There wasn't an Internet to go on and find out I wasn't alone."

But by part four, and probably sooner, though none of the cast is significantly older, we're in at least the late 1990's with TG stories on the 'Net, lots of explanatory material available and a number of Ts (and their supporters) in the story who seem to know who they are, what they're doing and where they fit in.

If you can, it'd be nice if you could resubmit part one for more consistency with the rest.  It does mean that your protagonist's alter ego is checking in from 2025 or later, and that David, living in the '90s, never tried to look at the TG stuff on the 'Net until she confronted him from the future.  But that would seem to beat the current situation, or the alternative where Older Tanya has solved David's problem by reformatting the world in such a way that the story's happening a quarter of a century later than it did originally.  Not that she isn't capable of doing that under the story conditions, but then it's not really the "Do Over" your title describes.

This story is coming along very nicely!  You got my heart back in my throat in the hitch-hiking scene, but resolved it very nicely.  Not sure I buy the little secret CD faction that seems to exist at school, but it's a nice fantasy, although not as much as the impending sleepover!  That has marvelous possibilities.  Also, can't wait to see what this camp is all about.  Keep up the good work!

Really nice start.  Looking forward to part 2.