Actually I thought "I'm not a biologist" was quite a sensible answer.
Most of us who are not thoroughly immersed in the debate have never really thought about exactly how one defines a word like woman, really. We just know we are and have always been and always will be. It isn't something that most of us ever think about putting into words.
And then when you start to become aware of the whole debate and the minefield around what exactly you say, you realise that this is somehow going to be seen as a 'trick' question. You don't want to mention physical attributes/organs, because some might not have them, you don't want to get into hormones, same sort of thing, etc - those sorts of things are fraught with difficulty. And just saying 'adult human female' sounds simplistic ,because you'd expect that the person would then say 'ok, define female' - it sounds like they are asking for a specific biological definition, how can you tell exactly, etc. And for a lot of people, they wouldn't really know.
Of course someone in her position should know that it's a huge debate at the moment and probably have prepared something to say.
But I do think that some people who are really immersed in the debate have lost sight of what the average person probably thinks if they're asked to define a woman. It just seems like such a bizarre question that many might not know how to answer - female seems too simplistic, since for most people, it just means the same as woman, and thus is circular. And beyond that, you might have to get into some very specific biological facts, and they wouldn't want to claim to be an expert in that either. And for normal day-to-day purposes, it just isn't something that needs definining!
So I have sympathy (to an extent) for someone finding that question difficult. I'd probably flounder if I was asked that question too, wondering what on earth the questioner was actually after and what hidden meanings there were.