When (if ever) is it ok for a parent to ask another parent friend if they are having more kids?

Not sure how controversial this is, but I know conceiving/number of kids is usually a touchy subject. So the question is pretty self explanatory but, here is the situation (which is real).

I have a friend that I met a few times but we interact a lot on social media. We have known each other about 8 years now, have hung out a few times and talk on and off about our lives, kids, etc. she is definitely more than an acquaintance but not a good friend.

She has one daughter who is about 2, and sometimes I wonder if she’d like to have more kids.

I ALWAYS err on the side of safety- have never asked her about it, and generally refrain from any personal questions unless I am bffs with someone. The kid question can often be a loaded and sensitive question, but I was wondering if it makes a difference that I am also a parent, and a friend?

Thanks!