Quite frequently the best answer to a problem is user education. Are 1 or 2 employees giving out the password to other people, do you spend spend several 1000's of dollars on a Secure ID system so passwords get invalidated after every use, or do you tell the two people "Hey, you need to stop doing that or you are fired" first and see if the problem stops?
Some times the best solution is not a technical one, and if a person did not ask for a non technical solution you should still give it as it is the best option. In the OP's question the best possible answer would be "Talk to your girlfriend and don't try to hide it."