My gf was raped when she was little?

My GF of 7 years was raped when she was little, were planning on getting married soon but she never told someone except for me and someone else. Its been a problem since we dated, shes very upset and she thinks why did it happen to her a lot. She refuses to tell someone she thinks its just in the past. It also affects me and I try and tell her to get help but she refuses and thinks she is just perfect. Any advice?