I feel like the Miyoo Mini is a bit overhyped at this point. The original had a nice size and feel to it, solid custom firmware with GarlicOS, and lots of fan made physical add-ons like stickers and 3D printed cases to personalize your device but you can't really buy it anymore and while there is the Plus variant that added WiFi that sounds a bit overkill for what OP wants.
Ah okay. Well if the problem you foresee is if she can understand the menu and how to navigate the device you could install the MinUI OS which is quite basic.