Penny de Valk's Answer:
Your natural instinct in this situation will probably be to take offence at your employee's criticism of you but, in fact, the primary issue to address here is that your employee's behaviour was unprofessional and inappropriate.
As a manager, you need to separate the two and start by conveying the message about what is and isn't acceptable behaviour in your organisation. It is inappropriate for a staff member to be talking to a candidate about another member of staff, whoever that might be, in a negative way.
Ideally, the manager who overheard it and raised it with you would feed back to their colleague that they don't think it was appropriate to talk to a candidate like that – if possible, encourage them to do that and help them figure out a way to have that conversation so it doesn't interfere with their relationship with your team member too much.
It is particularly important to encourage your fellow manager to speak to her if you are to consistently signal to new staff the standards of behaviour that you expect and reinforce the message of 'how we do things around here'.
When you yourself speak to her – which you must – you would ideally want to be able to say, 'You were overheard saying…' so if that doesn't identify the individual who heard it open with that. If asked, 'Who heard it?' reply that it's not important, and rather what is concerning you is that she feels it appropriate to be critical about another member of staff to an external candidate. Check that she did say it and, if she acknowledges that she did, keep reinforcing the inappropriateness of the behaviour.
Assuming that she understands that, regardless of whether she agrees with it – remember, you are explaining a standard of behaviour, not negotiating – then you can address the separate issue of the content of the criticism.
Ask whether she would like to give you some direct feedback as you were disturbed by the content of what was overheard. You can then hopefully have a direct conversation about how she finds your management style.
At this stage, just listen to the feedback as there may be something in there that you can learn from, take a constructive criticism approach and make sure you end your conversation with some key commitments from you both to improve your communication in the future. Be sure to document the whole meeting.
To follow up you might want to think about using a team meeting or development day to spend some time talking about what constitutes professional behaviour.
Tackle it directly. Say to the bad mouther, 'somebody heard you speaking negatively to the candidate'. It will cause them to stop and think and the ripple affect of their conversations and the perception of them by others. Lets face it, if you have a conversation in the office, you can't expect it to remain private. Let the team member know what the fall out of this 'advice' was, and that if she has issues with you to take them up with you not bad mouth you. I would also contact (or get HR to contact) the job applicant to followup on the candidate.
I have been working for a company for almost 3 years and, in the past year a new employee who started working there, has been harassing me by being rude, disrespectful, he tells my boss that i don't know how to do my job and that they need another person, because i relay messages to him from his clients, that they are complaning that he has not returned their calls,so he gets up set and bad mouths me in front of other enployees.