Keychain passwords copied to another mac user

I have had my MacBook Pro for a few years. I have iCloud Keychain enabled on it for a while. Recently i created an account for my wife on this mac. She setup her Apple ID and her iCloud Keychain was also activated on this mac. Then after a few days all my passwords started to show up in her Keychain on the Mac! Then after checking we noticed it's merged with her iCloud Keychain passwords! Can anyone offer a help? It's ridiculous in terms of privacy and security!