Wow, I thought this was going to be easy to answer, but…! Not many cis-women are open to their mates being transgender. I base this on my last two marriages and other relationships I tried to start. Based on how you worded your message, I would say she believes if she ignores it long enough, the ‘phase’ will fade away and she will not have to deal with it. You can do all the explaining possible and they won’t budge.
You also feel this woman is meant to be with you? You may be mistaken and do not want to accept it as such. She may love the man she met, not the transgender woman you prefer to be around her.
I met a cis-female, I should say she met me on a transgender dating site. She wrote me and had been in some sketchy relationships, both male and female and figured I would be good for her instead. Well, 1.5 years later, we’re going strong. I may still be pre-op, but she accepts me as female. I feel like a ‘lesbian’ with her that I may have male genitalia, but she calls that a ‘bonus’. I have been on HRT for four years and it has helped my appearance as well.
Good luck with your relationship. I wish the best for you.