Make her install Gentoo in her own and make sure to berate her at every step /s

Personally I would go with something that has KDE so she gets fancy animations and stuff, but Mint is a perfectly valid choice too (cinnamon also has some cool stuff to toy around with but not as much imo). Just make sure to show her how to install stuff, and put adblockers and shit in the browser. Also highly recommend installing some of the linux games.

Last I checked they’re not very keen on repairability (Being able to remove glass and being able to fix everything are two different things) and sustaniability (and no making a phone more efficient/produce less ghg/etc does not mean caring about sustainability when your whole model is mass producing and selling new phones every year while encouraging customers to ditch their current functioning phones for the new one, sometimes by purposefully removing support for them or bricking them with updates)