Tough situation, but not that unusual. My suggestion would be to tell the employee that you’d be happy to talk about her performance and her salary with her but that you will not talk about another employee’s performance or salary with her. That is confidential information between you and each individual employee. You might also mention that there are many variables that go into determining a person’s salary/hourly wage and that it is not her place to try to pin you down on that personal information for comparison reasons. I would also suggest that you remind this employee where you’d like to see their energy going towards in the workplace and where it need not go. Lastly, I might make a general statement at one of your upcoming staff meetings about the value you place on cooperation, teamwork, and positive synergy amongst the department. You might even consider a teambuilding as well in order to put more focus on the working relationships and less on individual comparisons.

Should other employees begin to get caught up in the benefit/wages comparison game, then you will need to address it in an upcoming staff meeting and lay down the law in terms of your expectations around such discussions and comparisons. If people get that that is “not cool” to go down that road, they will stop, especially if eventual consequences result. Sorry I could be sweeter.