Puzzle: Two different account login passwords


Hi all. I need help from the collective Brains Trust on this one.
My wife has a recent model Macbook Pro 15" for work. Work made her change her user account login password about 3 weeks ago, which was all fine. She had to work from home recently, and it wouldn’t accept her account password to log in, but it would accept her old password. Back at work, and connected to the work ethernet network, it will only accept her new password.
What gives?
Possible clues: when logging in at home, we got an error message saying that there was an inconsistency between the Keychain password and the something-else (can’t remember what). So we had to unlock the Keychain (using the old password).
Also, we upgraded her from High Sierra to Mojave about a week ago.