Girls i need your help?

What does it mean if my girlfriend cries about every problem but when we talk about a certain problem she doesnt cry at all and i think its the biggest problem of them all. See when she was 5 her half brother was 11 and he made her jack him off untill they got caught and she says she doesnt remember anything even though she has told me a lot but everytime i bring it up she mentions less and says i forgot and then i would tell her but last time u told me more and she just keeps saying i forgot. i know she remembers but she wont tell. when she brought it up the first time she made a joke about it saying she was good at it cause she made her ***... now really who would make a joke about that. then she doesnt cry about it when i do cause i hate to think that she got used when she was 5. but now im starting to think about how she acts towards the problem like she likes it. any suggestions on how to make her tell me the truth of what happend that day? cause i dont even know if ur clothes were off that day and a while ago before she told me about this i told her i like that brother more than the other untill she told me than i ******* hated him, but when i told her she said she likes him more. i really think she likes the fact that she jacked him off and made him ***.