@Imtootired YANBU. Next time, say 'why on earth would you ask that?' with a
kind of look. What a rude cow! Why the fuck does she think she has a right to say anything about you and your pregnancy?!
As a few posters have said, some people take a woman being pregnant as a cue to be a rude ignorant cunt.
I had a myriad of shit thrown at me.
At 7-8 months pregnant: 'Christ you're fucking massive now' (from a male colleague of DH's)
'Rather you than me, been there done that, your life is over now' from a 40 y.o. female colleague who was childfree.
'Your fanny will never be the same again OR your sex life!' from a female colleague of my brother.
'Put on plenty of weight haven't you?' from a neighbour of my parents.
'Why did you go and do something so stupid?' when I told my aunt I was pregnant? (I was late 20s, married 3 years, owned my home, and had been in a well paid job for 9-10 years that I intended to return to.')
And just 2 weeks after I had HAD the baby - a male colleague of my DH's said 'not lost the baby weight then fatty?' (It was TWO fucking weeks since I had given birth.) DH said 'she's only just had the baby you fucking cunt' and glared at him. The bloke said 'oooh touchy much?' and waltzed off.
Also, 'can't wait to see YOU with a baby ha ha!' from a cousin of mine.
I also got a work colleague (on the first week I went back when my firstborn was 4 months old) saying 'pull your socks up, no excuse to be lazy and useless just coz you got a baby. No-one asked you to have it!' I wasn't even being useless and lazy. She just needed an excuse to have a pop at me! 
As I said, some people are utter cunts, and think they can say what they like, no matter how hurtful.
I had similar things said to me when I had my second baby.
Funnily enough, I don't recall anything being said to my husband - ever. 
Oh and btw OP, ignore the ludicrous comments about you being 'rude' by describing this woman as a 40-50 y.o.. nondescript woman. Some people just LOVE to come across as offended, and cause a stink for fuck-all. The 'professionally offended' they're called! 