For me, it‘s strictly based on Assumed Age; if I think she’s 15+ years older than me she’s a lady and if I think she’s 15+ years younger than me she’s a girl (I know that you’re legally an adult, don’t @ me). But regardless of context, if I say ‘woman’ my wife instantly wants more information – is it just a matter of insecurity? Again, I’ve never stepped out (though there was an incident a few months ago of a woman I know from work potentially trying to make something more out of a professional relationship).