Anonymous wrote:“Why? What’s wrong with this one?”
See if she gives a reason. The you can counter it or reply with “We can’t think of a reason either so we’ll keep it until we need another”
No. This response gives tacit approval her being rude. By engaging, OP would be sending the message that the comment was appropriate in the first place and that she looks forward to her MIL opining about everything else.
"Hmm. That's a rude thing to say when you're guest in someone's home." Then walk away.