Send a written invitation (or an e-mail with read receipt requested) to the employee you are about to terminate, detailing exactly when you want her to be in your office or a conference room in the human resources department that you have prearranged. Invite your human resources representative as well. The best time to deliver the news is at the end of a work day, perhaps even on a Friday. That way the terminated employee won't be humiliated by walking out in front of others.
Although a security presence usually isn't necessary, you should alert the person in charge of this function in your company. You may want to have someone standing by to ensure that the terminated employee leaves the premises peacefully.