As much as I hate to add some critical thinking into a religious forum. There is a metric fascinating ton of things going on in this situation that isn't being talked about in this article.
First of all, Montana Governor Greg Gianforte signed a law into effect making this illegal last year, he actually had his Lt. Governor personally investigate this, and she found that the law had been followed. Second, take the transgender stuff out of the situation, and it's still a dysfunctional situation that needs correcting before this kid dies. She actively trying to kill herself and the family seems unable to cope with it.
Second, the only person quoted is the (possibly evil, who knows?) stepmother of the daughter. The biological mother and father aren't takin'. That's weird (well, suspect, anyway).
Third, frankly, the journalism is lazy, I don't know that I'd take the stepmother's word on the subject if it wasn't backed up by the Lt. Govoneor's investigation.
Something horrible is going on in this family, and it's not that transgender part that's at issue from my reading between the lines here.