Analyze all the facts relating to the issue you were attacked on. This will allow you to make an informed decision before releasing any statements.
Avoid personally attacking your opponent simply because she did the same to you. This will lead viewers to believe that the original smear was truthful.
State briefly in either a statement, press conference or interview that the other side has spoken falsely and you would like to set the record straight.
Give the true facts surrounding the issue and state the possible solutions, ultimately choosing one and giving reasons for doing so.
Close by stating that campaigning does not have to be dirty by resorting to misstatements and falsities. To the contrary, the goal should be to solve important issues. You will naturally come across as the nobler of the candidates, level-headed and articulate.