MIL is not developing dementia: she's very old and frail but she's showing no signs of even slight memory loss. She is mentally razor-sharp.
It's very out of character. Normally, she is extremely reserved. She specialises in small talk ( hours about the weather, Christmas lights etc). In her world, is bad manners to talk about yourself and she doesn't really try to get to know me or her grandsons. It's just all very achingly, boringly polite and reserved and the visits really drag. She is so reserved that the DC barely know her despite having spent many, many long visits at her house over 16 years.
And then out of nowhere, she came out with that! She said it like she was being conversational. It's difficult to understand why she said it, but there have been other times over the years where I've seen flashes of the real person underneath the surface. So, my best guess is that she meant to be offensive especially as she didn't try to retract when it became clear that it made DS and me uncomfortable.
It's a strange thing to do and I'm annoyed with myself that she sought to undermine my son's self-confidence and I sat between them allowing her to keep repeating it.
And now, I just want to go home, but everytime we leave, I'm always conscious that it might be the last time DH sees her, so I don't want to ask if we can go earlier than planned.