I guess there isn't any way to gauge reaction from her, when you have the talk. Even if she is totally loving.. I guess -especially- if she is totally loving you, it will come very hard to her, very hard to accept. Mine cried for months, made it completely clear that my journey will be alone the whole time. You have been feeling this way for years, it is something she never saw coming. My wife's doctor, who she went to go get her Xanax from, told her, this won't be something that hits you between the eyes, it's something that runs you over from behind.
She will feel lied to, betrayed, conned, duped, every adjective you can think of, she will feel, she will say. idk if you can pin the abuse on being transgendered, as a way you were coping, your therapist might tho. I was abused by a relative, at a young age. My wife thinks that is why I am this way, as a means of coping, hiding, pretending I'm not a boy to avoid being abused again (no it can't happen anymore). Be prepared for a real storm, a backlash when she finds out, either by hints, mannerisms(which she would probably miss, mine did), or you just telling her. Your therapist should have some advice how to bring her in to your circle. Kids too.. There is no question they will need therapy to learn to cope with this, just as you are.
Who was it... Bette Davis that said "brace yer selves.... it's gonna be a bumpy night"?
Or I could be all wet, and she'll be totally supportive. That is my hope and prayer for you.