The issue is that many people, and in some cases our laws, consider trans women to be female. And as much as you’d like your opinion to be the only opinion, it isn’t. Nor is it any more valid than anyone else’s.
If you were to do a poll of the general public on whether this person was a woman, I'm confident the vast majority would say no.
As for whether this person is female, even genderists don't believe that. At least, they claim to acknowledge biological sex - and female refers to sex, not gender identity. Logically that means TRAs don't think transwomen are female.