Why not make them executable and stick them in bin

Plan9 mothra

Gnome browser, I’d use ladybird but it’s not ready yet

You can install imperatively using nice profiles. So you the OP can set up the base distro in a way their SO can’t break. Then any extra software can be installed imperatively using nix profiles. Any installed software will work as normals. Checking the normal places for configurations if their SO even needs to go that far

Nixos with whatever defaults you don’t want her touching, then she can use nix profiles to install extra software if she wants

N I x o s

Xournal++ works pretty good in my experience