This. ^
I know a woman whose daughter Hannah (when she was 17) told her she was dating a 19 year old transgender man. He was born female, and had been dressing as and presenting as a boy from the age of 13-14. Then he started taking hormones and going for the full transition when he was 18. He was going to have top surgery at 20...
This woman said that she acted fine when Hannah told her that she has been dating Liam (born Lucy) for 4-5 months, and said 'that's nice dear, Liam seems nice.' But when she was on her own later, she cried, and cried, and sobbed and sobbed. She was worried about Hannah's future, and the prejudice and hatred she and Liam would get in the future. She knew that their future would be difficult and full of pitfalls.
Why did she react like this? Because she was a raging transphobe? No, because she was worried and concerned for her daughter - her ONLY child. It was a shock.
The relationship lasted a year. Liam went to University when he was 20 and Hannah was 18. (She didn't go to University, she got an apprenticeship with a big company in town and was going to have a long distance relationship with Liam, seeing him every couple of weeks, for the time he was at University, and spending some weekends with him.) He didn't go til age 20, as he'd taken 2 years out after college (and worked part time) because of his issues, his transition, and his low moods. He decided against the top surgery at this point (had small breasts anyway) as he wasn't in the right headspace for it.
One and a half months into starting University, he phoned Hannah and ended it, saying it wasn't working. He said he's not in the right place for a relationship, and he needed to be single and alone, and that he wasn't seeing her again. Hannah was devastated .... Her mum cried with relief. (She never let Hannah know how she felt at ANY point. And she said (to Hannah) that it's a shame that she and Liam were over...)
6 months later, Hannah started dating a man the same age as her (he was born male.) They dated for 3 years then finished. 2 years later she met someone else a year older, (also born male,) and 4 years later they are getting married (in 2 weeks.)
So @nowhatx what your daughter wants now, may not be what she wants in a year, 3 years, 5 years. You are going to have to let her make her own choices though.... All the best. 
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