The best solution for her dilemma might be writing the pin numbers down in one list and keeping them in a safe place at home. This is the most secure method to not get stolen because it would be only just one list with no chances to get copied and she would be the only one in knowing where it is. Keeping them on her smartphone does not seem like a good idea because it can get hacked, or stolen, or accidentally copy it and send it by mistake to someone, so to avoid this kind of problem, the old fashion written list is the best option.