Do not overcomplicate it. Have a box or a “place” near the front door, mine is in my dinning room hutch, and keep everything important in it that isn’t used daily. Do not overcomplicate by trying to file things or have “organized” separate locations. Also, a wallet that is connected to the cell phone (Otter box has a great one) is a huge help. Place bus cards or credit cards in it and use an app to find your phone when it is on silent (icloud’s find an iphone or findafriend app). My husband is a great help to me by being there with cash when my ADD symptoms are bad and holding onto my extra credit card so I only have to keep track of one credit card and my license. Take pictures of her cards so she can put them on hold while temporarily looking for them without starting a new account.
She may always occasionally lose something and you can’t expect perfection. This happens to me during times of high stress, but things can improve significantly and be less frustrating for the both of you. You can be a great help to her but simplify…simplify. Good luck.