Blocking out memories?

I am trying to help my younger sister find the baby she was forced to give up for adoption. This happened back in 1969, and she was only 15 at the time (14 when she became pregnant). She has little, or no memory of the actual pregancy, no memory of prenatal visits, and only a few scattered memories of being in the hospital. No memory of the actual labor and delivery. Our parents have always refused to speak about it, and they are both old and sick now, so we can gain no information from them. My sister is tomented by her "lack of memory" and I know she feels so inadequate because of that. I think it's due to the trauma she went through and also her very young age. How can I help her to get through this and comfort her as she struggles to remember what she just can't remember? I know she feels tremendous guilt because she just can't remember ... Any advice is appreciated. Thanks! Aunt B