Hi Magic Dad.
I'm Mom to an older trans* girl. She came out to me last year just after turning 19. I was raised by a single Dad, myself. I am proud to be a non-binary woman. Yes, I am a cis-female, but I grew up in a mostly male socialization. That being said, I hated dresses, eventually wore my hair proper short, but always knew I was a 'girl'. That should have made it easier for me when my child informed me we had been doing it wrong for so long.
I cried to lose my son. I cried because we didn't know sooner. I truly wish she could have understood sooner so the transition would have been more seamless, without the testosterone playing havoc.
You have this opportunity. She's still young and on her way with an amazing Dad who cares enough to come hete and find out more about this journey. I understand the sense of loss of your dreams and possible negation of your efforts to make your child a successful man. She now has an advantage of having a parent that can show her that gender identity is not a measure of anything. Your head may swim, but she's been coping with this for a while.
I believe eventually you will learn your child hasn't gone anywhere. Your preconceived notions are what go out the window. Yeah, I believed I had done something wrong along the way. But this is about your child and her path to success. You're doing it well and lovingly.
I know you will cherish your child no matter what path she walks. You've come a long way and are an awesome Dad to be supporting her.
Please, keep coming back.
Ps: our little family had a wonderful holiday in London last year. My husband marveled at a sign on a bus that said "Some guys wear dresses, get over it". It looked to us like more folks "get it" there than here. Wishing you well.