Hey collel, I see what you are saying.  Your sister was most likely mentally ill and it's a major nissayon for you to overcome.  I believe it is commonly said that that the way to transform these experiences is not to bottle them up and isolate yourself, but rather to face your deepest fears and share your struggles with others, eventually helping other Yidden who have been in similar situations.  Then, all the "aveirot" are mamash transformed into "mitzvoth", because you are able to pull every type of Jew who has been similar afflicted with these difficult and painful incidents.