This is a hill my husband and I willing to die on in our house.
Funnily our second oldest daughter formed the same opinions as us in school from watching so many of her peers identifying as trans. Since it was her social environment she built her own beliefs that it's attention seeking behaviour fundamentally forming new "cool groups" of being sooooooo different and hard done by.
She thinks the world has gone absolutely crazy to be honest and she's early 20s.
Our next daughter is much more likely to fall right down the rabbit hole. Because she's highly emotional, likely on the spectrum and would probably believe the sky was green if her group of friends cried and told her so.
Teens clash with their parents usually over some type of what they consider outdated thought process on what ever is deemed socially excluded order of the day. Be it music, or social changes.
If one of children decided in their teens they are trans. We won't support it. They can dress how they want call themselves what ever they want but we won't be referring to different pronouns, if it lasted until adulthood they obviously can choose to live how they want.
Sometimes you just have to state how you think, the boundaries you are willing to allow them move in and then leave it.
Depending on her age though I would be considering carefully what she is interacting with online and monitoring it.