You start with a light bike that fits her needs, add a lightweight, reliable motor, and a removable battery.

SFAIK the Faraday battery slides out easily and is not permanently mounted. But the bike is limited in scope.

IMO, selecting components for the job and an easily removable battery is the best way to handle the need, as very few pre-made bikes are in the range to choose from.

Friction drive might work, but in most cases, won't. She might be a rider in Chas58's class, but very few women are. A folder might work, if the compromises involved are not too severe; IMO, they are.