Tbh I wouldn't consider claiming to be non binary 'coming out'. If she decided she was actually a boy then there'd need to be some chats but non binary is just 'I don't like being identified as a woman'.
Aye, pal good luck with that xD
This one is mostly a phase and will pass.
But it would be good to have lots of chats with her about things like internalised mysoginy.
When I was young I was probably the equivalent of many trans youth today (only without the social media to further influence) Largely because I didn't feel i identified with my female classmates. And because my boy friends said things like 'girls are bitchy/gossipy/always overreacting' so I felt it was wrong to want to be a girl. I hated my female body, I dressed masculine, I was not interested in boys or boy bands or girls toys. All the hallmarks.
Now I look back and realised that internalised mysoginy as a result of the people I was around and the overall societal view towards woman, played the biggest role.
But by the time I was 16, I was over it. Not necessarily comfortable in my body but what teen is? I definately didn't want to be a boy anymore. I feel for teens today as I suspect many of them are not trans but cannot escape once they get thr idea they might be, due to the influence of social media. There will be so many young girls detransitioning in a few years.
Anyway, I digress, try not to worry too much. Just do all you can can educate her on womens rights and struggles as much as possible. Because she is still biologically female and the world will see her as such whether she likes it or not and she will have certain things imposed on her and certain disadvantages as a result whether she wants them or not.