my mum is the same age as yours and i remember her making a comment like this years ago... not sure why i remember it but we were at a pool and there was a preggy woman with a bikini top and shorts and she said something similar about how wrong it was and that lady should be covered up!!! If it comes up again, it'd just do a really good scoff and say "it's not 1957 mum" - make HER feel all old and out of date. Or a real condescending "oh, yes granny" hahah

I must have only been a teenager but that's how much it struck me as a strange thing to say!

If my stomach wasn't white as a sheet compared to the rest of me (and me booobbies actually fitted into my old bikini tops ) I'd wear my bikini, with shorts or a sarong.