"I still lurk from time to time but haven't bothered posting much the last couple of years."
You and me both!
Anyway, I was wondering if this was going to be like an ongoing show, or just a one-shot miniseries? Because if it's ongoing, I'd could see that being the justification for aging up the character. An 11 year old actress won't be able to pull off an ageless vampire for more than about a year (just look at the cast of Stranger Things now!), but a 17 year old is already grown up, and could probably maintain her look for at least a few years.
Still sucks, and I'm probably giving them too much credit, but that's a possible reason that doesn't depend entirely on political correctness.