This sounds like one of those leading questions I've gotten when I accidentally found myself in a TERF lesbian space. The followthrough isn't pretty. Let's not go there, m'kay?
I am because I am.
I am because parts of my neuroendocrine system run much better on estradiol than on testosterone.
I am because regions of my brain around the hypothalamus seem to have female-like structure and activity patterns, rather than male patterns.
I am because a drug I was exposed to in utero likely flipped some genetic switches in differentiated stem cells prior to development of some tissues.
No, I don't have a uterus or cervix. Yes, I get my estradiol through patches. All of this is identical to what a woman who has had a total hysterectomy has to deal with. Are they women, or not?
Edit: I am a woman because I wear high heels and makeup (but I don't identify as a drag performer, Elsie!)