Lots of ignorance going around though on twitter, she isn't trans. She has Swyer Syndrome, which means that while she has XY chromosomes, she was born with female reproductive organs thus was asigned female at birth and has lived her life as female.
It is one of the conditions that can fall under Intersex and shows that "biological sex" isn't cut and dry either.
A similar situation happened with Caster Semenya who almost got disqualified in 2009 because people where accusing her of being trans, when it turned out she had a condition where her testosterone levels were that of a male