It's so tricky when mothers/ mil start nagging about stuff like that. It's just that kids had to be dry at a certain age in the past and probably because parents wanted their child out of nappies when they had terries and limited washing facilities ( inn talking my mum - yours could be younger
)
I think unfortunately it was seen as a sign of good parenting or something.
As everyone says they have to be ready. I always think there's no harm in getting a potty out in the bathroom and getting used to the idea of toilet and the language around it etc would that keep mil off your back?
I get the idea around terries etc but think that works for any nappy without a stay dry bit too.