It's almost laughable that someone could have made it through parenting to the teenage years and still think that telling a child they're wrong and trying to forbid them from interacting with the new group would actually work.

And they clearly realize from the letter that the kid's reaction to this identity is, itself, a problem, and a sign of underlying struggles, but they aren't able to make the tremendous leap from there to the idea of a therapist, even though the kid brought it up?!

It kind of sounds like this parent is one of those people who doesn't really "believe in" therapy, but it's been a whole generation since I dealt with that problem in my parents; it seems a lot less likely today.