While simple, it can honestly be kind of fun to just go in and let them know. When I was recently laid off, it went something like this.
HR: “I know this might be a shock–”
Me: “Yeah, you’re letting me go, I know. Here’s my work laptop and badge, I’ve got all my stuff in a box outside, what do I sign? Trying to catch the next train home, so I have like 20 minutes.”
It totally threw off my boss and the HR lady trying to do their sombre, dignified thing, and was pretty funny to watch.
Go to another account she hasn’t messed up on her phone, and make her watch as you use the password manager to get in. Then, you can tell her for sure that the tech is working, and you’ve done your part, but you cannot fix her behavior. If she wants to keep resetting her passwords all the time, that’s on her, otherwise, she’ll have to put a small amount of time and effort into adapting to using the password manager.
If she isn’t going to follow your suggestions and advice, why is she asking you for help? If she sincerely wants help, she needs to make an effort on her side to follow through.
This is a problem with psychology and boundaries, not a tech issue.