Mum had been resisting the idea of nappies (although she was the first to propose the idea), but when I told her we wouldn't buy nappies, we'd buy 'disposable knickers' instead she got on board.
I agree it is better to use the term disposable pants or knickers than nappies. The majority of people with dementia still have a long term memory even if the short term memory has gone.
Nappies are for babies and the term could still cause upset.