Omie5rau

Only benefits I see is battery life and google not knowing the device location, but those do not concern me that much.

I think Dell you can configure without Intel Management Engine(Intel vPro). Lenovo and Dell both use Intel WIFI which needs non-free firmware and the fingerprint scanner probably wont work at all (not that you should use it anyways). I trust neither company, but both make nice machines.

Samsung Galaxy S9 is best LineageOS supported phone that I know of, with features like water proof, small size(good for single hand use), good camera... Only bad feature on S9 is edge screen(but you get used to it), and glued battery (still not too difficult to replace or take to professionals for less than 100€. Might lose water proof if you replace the battery).

Installing Lineage was bit more difficult than previous phones I have done, but doable by following instructions and repeating them as things act wrong.

You need global model, not sure about carrier locking other than mine which was "DUOS" and it did work, found mine used year ago for ~300€.

I would put her on Debian or Fedora with Cinnamon or KDE desktop. Upgrading those is easy, and Fedora or Debian(Testing) has already quite up-to-date software, if she needs very latest for some reason then use Flatpaks(should be easy with kde discover). I would not recommend Arch based distros as pacman does not hold your hand. Also they add questionable sponsored software (manjaro), they also host non-free software that breaks Linux workflow and does/can do bad stuff.

Knew Brave was malicious, from it not being available on official repositories on any trusted distro.