Wife admitted she had incest with her brother

I am devastated . I am 34 she is 31 I have a 4 year old son. We got married 3 years ago, been together for 5. We are both from small towns in the countryside, so we know each other's families. She has always been a very kind and respectful lady. Yesterday I asked her what does she think about incest, if she would say it's "ok", or if she despises it. She was watching tv in the couch, she didn't answer right away, she just looked at me with a weird expression. She said it's not ok, but it's a natural fact that people in the same family are more likely to be attracted with each other. She said that in a very vague way. When I sat down near to her, I noticed she was breathing faster than normal. I pressed for more, she started to look at the floor and said "I've been attracted to my brother" I insisted that she finishes, she said that they had some "kind of sex" when they were teenagers. I was in shock, I didn't say anything. She started to cry and telling me that she was sorry. She said she was not expecting to find love again after what her brother did to her. I don't want to believe what she said, and it's killing me that I'm doubting her words. I am 99% sure that she is lying and it's all made up, but it's that 1% that is gaining me at this moment. She is not a liar, will never fabricate anything like this. I am all over the place. She invited her parents to come to our house tomorrow, I didn't say anything, I am too hurt and I don't want to destroy her life in case it's made up. How would you handle this situation? I am really hoping this is all made up to get some sympathy or to make her parents proud. What is your opinion on this matter?