Come on now, most will ask if a woman is married or has kids, it's just social chit chat.
I think in 2023 this is a bit out of touch and very dated for lots of reasons
First there isn't really an expectation any more that a woman is married or has children. This question really only tends to come from older married women who are a bit out of touch.
Second the whole #bekind movement - you don't know who you are talking to, there are plenty of people who wanted children but couldn't have thtem, rounds of £££ failed IVF, plenty of people who suffered bereavement and this kind of question is on a sensitive subject that is very distressing for people.
Third, I think now it is more conventional to wait for people to volunteer that information themselves. Similar sexuality - how on earth you know she is not assexual blows my mind. I hope to god you didn't ask her. If anything I feel sorry for her being put in a situation where she felt obligated to reveal this information to a total stranger
Fouth, there are a lot of people who are child free by choice and have fulfilled happy lives without the kind of problems that come with being married to often selfish men and having to raise children. Statisically single women are much happier than married women; unsurprisingly married men (catered for) are happiest. Asking the question is dated anyway but persisting is basically putting someone in a situation where they are feeling obligated to justify their life choices to you which is rude.
Whatever you say, given the whole tone of your post, I bet anything that you conveyed to her that it was in your view a terrible thing she wasn't married and didn't have children (which itself is a bit of a sad world view) - whether by your further questions or even by body language by a little tilt of the head, microgestures, and soft "oh".