I’d start with a cell phone first. The last thing you want to do is give up your life to google and microsoft. Get yourself a graphemeOS compatible phone and replace all the apps with open source solutions. There is a (very very brand new) app called Vela Maps that acts just like google maps, only you can choose not to talk to google servers when you do.

Use sync-thing to auto upload photos to a server you control, even her home PC

There are ways to change the linux desktop to look like apple, though I don’t know what they are. possibly KDE?

unfortunately only google pixel tablets work with grapheme OS. There are tablets that are compatible with ubuntu touch

As for the watches, I don’t know of any that are de-googled.