I believe its a pretty simple question to ask and I believe it was easily appropriate.
Women have two X chromosomes and are capable of pregnancy and giving birth from puberty until menopause. Female anatomy is distinguished from male anatomy by the female reproductive system, which includes the ovaries, fallopian tubes, uterus, vagina, and vulva. The adult female pelvis is wider, the hips broader, and the breasts larger than that of adult males. Women have significantly less facial and other body hair, have a higher body fat composition, and are on average shorter and less muscular than men.
We all know where that question was heading, she needs to answer that question.
Oh I have no doubt that she CAN answer the question. But this is about a courtroom, where definitions have more serious consequences based on how they are defined. It's not a biology class. In a biology class, she can state chromosomes and every other biological criteria that defines a female.
It's kind of weird, but when you craft LAW, it's not strictly a matter of science, but on how precedent has ruled and how law is applied. Even in my job, strict designations on what is a house, a residence, a job, a household, a company or establishment and so on - there's defining it for general understanding and there's defining it for law. Or TAX purposes.
She wasn't taking the bait. And I agree. Senators WANT to try cases in the Senate rather than in SCOTUS, and the followup questions would ALL be applications to law that has not been argued. Have you heard of the Ginsburg Rule? That's where SCOTUS judges aren't expected to give an answer on a subject they are likely to have to RULE on. To have any kind of integrity - the followup questions would all fall in that area.