I did. She doesn't define "sex class" anywhere.

And of course she doesn't, because she can't. She has a middle-school grasp of the subject, and she's trying to define "woman" as "woman" by using the weasel word "class".

I believe a woman is a human being who belongs to the sex class that produces large gametes. It’s irrelevant whether or not her gametes have ever been fertilised, whether or not she’s carried a baby to term, irrelevant if she was born with a rare difference of sexual development that makes neither of the above possible, or if she’s aged beyond being able to produce viable eggs. She is a woman and just as much a woman as the others.

I can only deduce that "sex class" is some kind of group where you produce large gametes, but it doesn't matter if they're viable.

I don't have ovaries, but I had them at some point in my life. I can only surmise I'm not in the "sex class" woman according to Rowling, since I don't produce large gametes, viable or not.