@julian @Blort thanks, but I decided to let it go.
Neither my phone nor my mother in law's is officially supported. There are unofficial ports, but the security patches are also at least a year out of date.
I'm also not willing to risk this when she's only here for two days. I'd rather have her leave with a still functioning phone.

I'm thinking about putting #LineageOS on my mother in law's phone. It's pretty old and my intention is to make it a boy more secure and maybe less laggy.
Should I be looking elsewhere or how does #LineageOS perform on older phones? Maybe an even more basic #Android install if I can find it?
What are your recommendations?