She doesn't identify, she's had gender reassignment surgery. I'm not a big follower of UFC but I heard Joe Rogan talk about it, and he goes on about her bone structure, density. It's an unfair advantage basically, reaction times are faster, she's stronger, punches harder, to the point where it is a ridiculously unfair advantage
The two cases are completely different however, Caster Semaya has a condition where her testosterone levels are way higher than a females should be. It's a horrible case, her achievements are being overrun by the scientific, and ethical shitstorm. And you have to feel for her opponents who obviously feel that it is unfair to them