How do i stop my timing chain making a noise when the engine gets warm?or d?

My Daughter has just passed her test and she bought a nissan micra 16v N reg.Everything ran fine on her way home from buying the car until the engine got warm,then it started losing power and making a rattling noise before stopping.The timing chain has too much slack in it and is upsetting the timing.Can this be tightened or will it have to be replaced?if so where can we get one?