Who is Catherine Marsh from Salem Falls and what is their importance?

Catherine Marsh is the girl who accuses Jack St. Bride of having an sexual affair with her while he is teaching at Westonbrook Academy. She has a crush on Jack and wants to believe the affair is real. Her father finds her diary, where she has written about Jack. She later tries to convince her father and lawyer the diary isn't true, but no one believes her. When Gillian accuses Jack of rape, Catherine comes to the trial and testifies that Jack St. Bride never touched her.