carlsson

Dumb question, but have you thought about getting her to use a password manager?  My mother was doing similar stuff.  Got her to start using Lastpass, problem solved.

Then again, a free lunch is a free lunch, so...

The bank doesn't use simple passwords. It uses QR codes + personal passphrases ideally entered on a different device than the one you're accessing the website on. As it turned out, everything worked as it should once I followed the same procedures she uses to, and it worked for her too today.

Possibly it was a random website survey popup that interfered twice with the login process earlier in the week. Those random "how do you like our site?" popup surveys can be a PITA even for experienced computer users.

Oh, yes.  I really loathe those pop-up messages even with adblockers activated.  Especially those that lock you out of a website with adblockers active.