Have a conversation and listen to her. I’m guessing that her behaviors are driven by an emotion. Maybe she’s overwhelmed by the complexity. Most people who say that they don’t care about security actually prioritize ease of use over security. Unfortunately good security can be hard.
If/when you speak to her, don’t try to solve her problems during that conversation. Meet her where she’s at and empathize with her. When she’s done, you get to express your concerns and see her reacting. I’m guessing that you’re concerned that she is putting her finances at risk. Explain your concern to her.
Once you both come to a shared understanding, then you can come with some ideas for her to react to. Again, dig deep into her concerns, talking through them. You’re going to need to let some things go. It’s her life and her money and you’ll be there to help in a nonjudgemental way if anything bad happens and then you can have another conversation after the dust has settled.
I ended up with my parents having 3 passwords. One for their bank, one for their health stuff and one for everything else. The bank and health ones are long and difficult to guess, the other one is easy to remember and “good enough”.
I stumbled into the Superbowl forum from a link in another comment and thought it would be football memes, but was pleasantly surprised by superb owls. Coincidentally, the power went out that same evening in the wee hours of the morning and with all the noise in the house muted I heard an owl hooting from outside.