Ive been deeply entrenched in the apple ecosystem, and I did eventually switch. key for me, similar to what other people said, was to switch the programs/ apps first. by moving to Firefox (zen), thunderbird, Libre office, Obsidian/zettlr, immich and the likes on apple first, I was able to swap out the OS without the need to relearn much.

so, my recommendation would be to get her the replacements, step by step, and give her time to get to know them, whilst having the previous defaults as fallback.