Would an autistic teen with the mental capacity of a 3 year old wear diapers?

The reason why I am asking this is because it's for my screenplay (which I have been working on for years, inspirational story too) about a man who takes in a low functioning autistic teenage girl with the mental capacity of a 3 year old. She was verbal (repetitions and toddler like talking), however drank from a sippy cup, had childlike toys, was able to feed herself, dress herself but needed help with ons, didn't know how to tie own shoes, and had to hold caregivers hand when going out in public due to wandering. Nothing stupid, sorry if it sounds like a dumb question but also I'm asking about this in general. As I also went to high school with a girl who's sister has low functioning autism with the mental capacity of a toddler but was verbal. I realize everyone is different on the spectrum as I am on the spectrum (high functioning autism).