The knob should just pull off, but sometimes they require full chooch. If she breaks it, it’s not a big deal. If Habitat Re-Store is a thing near her they usually have a shelf of these knobs for almost nothing. If not the big box stores sell them too, and the lights can be turned on and off without the knob until she can get a replacement.

Back when I worked as a handyman I used the old knobs for many things. Some people get very weird about change. I’d usually ask if they wanted the new one to wedge into their junk drawer, though.

Hollow doors have about a 1" frame of solid wood around the perimeter.