If I were to write a letter to my mom, coming out as a transman...

What should I write? How should I phrase things?

She's a manipulative narcissist with borderline personality disorder who threatens to delete herself when things don't go the way she wants. She also told me xmas 1,5 years ago she never wanted a son. Only daughters. As far as she knows she has 4 of those.

I'd love to not have her in my life anymore, but I'm too scared of her. I have avoidant personality disorder, but my sisters who don't have that are also scared of her, so...

Any help/tips is appreciated.