I understand from you that your sisters unpleasant memories relate to incidents/hurt/ anger experienced from her live-in boy friend. She now wants to forgive and forget. This sadness is causing her to feel more and more depressed everyday. Please correct me if I'm wrong. I would need to know specifically a little about what happened between her and him. Who broke up the relationship? Did she feel angry towards him? What does he feel about her now? Is he open to making up? Generally speaking, whenever we lose somebody close to us, we go through feelings of sadness, heartbreak, & bereavement. We then typically go through a process of mourning for that loss. Over time this mourning ceases, and you are then able to get on more with your own life, leaving the past behind you. Time is then always the best healer. You need to give it time and get her mind onto her daily living schedule. She should avoid sitting alone and ruminating all the time, but instead engage her mind, get out of the house, do some regular cardio exercise.