A decent compromise might be to pick a short phrase she can remember, and make all her passwords that phrase+the name of the service.

Like her bank password would be “iloveop+bank”, her Netflix would be iloveop+netflix", etc.

My mom’s password manager is a pen and paper notebook. It’s not ideal, but it keeps me from having to reset everything every month, and she chooses slightly more complex passwords since she doesn’t have to remember them (even though she is slowly memorizing them)