My elderly mom has the same problem. But her dying iPad 2 was already on iOS 9, and that GUI was already difficult for her. With each release from iOS 7 on, things constantly changed, and elderly people simply can't cope with change, I've learned. They learn something, or expect something, and now it's suddenly different (even if it's just surface level, it is very difficult for them). She always refers to the old iPad (1) as the one that did things better. iOS 4 to iOS 6 was her OS (buttons and things were more "3D"). iBooks app with the wooden shelves was very easy for her to understand and she could flick between categories by flicking between shelves. The current iBooks app is very complex if you want to switch categories. There is a higher level of thinking involved that some elderly people can't do if they never in their life dealt with computers. The current music app has very small targets for play and pause. She can't see them well enough. And there are many more difficulties.
Yes, you can turn off multiple apps, but you can't turn off multi windows in Safari. You can't turn off multitasking gestures like moving from the bottom of screen and up. But she just has to deal with all those things. She's frustrated a lot. So a device that could help her read a little, and do stuff independently becomes a source of frustration and she constantly needs help.