Thank you for your suggestion. My mother has declined adding a case because she carries the ipad mini in her purse when she is out. She doesn't want the additional bulk. She knows she is "not holding it properly" and moves her thumb if it's not responding to her.
I've seen people using finger loops that are stuck onto the back, or straps. I managed to find a decent looking instance of the latter in a quick search (so, just the first I found):
