First of all, let's get one thing straight. I am a woman. I was born with a penis, my body followed the typical development for male bodies, and more than likely, I have XY chromosomes. But I am a woman, and I always have been.
A trans woman is a woman (and she never wasn’t a woman)
Q: When does a trans woman become a woman?
A: A trans woman is a woman. She never wasn't one.