Whether it is you DiL or your daughter (or Son/SiL) the rules are, they're their children - their rules. Step over this line and you might get your fingers burned. It is very frustrating at times when you think that your advice might make life easier for them but never give it voluntarily - wait until you are asked.
Mandelson failed security vetting. Starmer says he didn’t know
My DGC was part-trained from 2 yrs but just couldn't be bothered - lots more interesting things to do! - so went to nursery in nappies. At 3 1/2 yrs, I guess felt different from little friends, decided to give up nappies and use the toilet. All very relaxed and much more so than the constant trekking to the potty/toilet with younger ones. I have to be honest, I didn't approve at the time but it worked out fine. I'm learning to keep quiet!