Advice please! Idk what to do. Long! Please read.

I didn't know where else to post this, but this seems like the most logical. And I don't even know where to begin. Im just so stressed, and I don't know who to go to, I'm just freaking out! So I was majorly cleaning everything, moving things around, wiping things down, everything. So I was in my movie closet breaking down an old movie case it was a bit taller then me so I bent it down a bit and a little book fell on me. It was just a tiny drawing book,it literally could fit into the palm of my hand. I opened it and it said a book about me and gina, by liz.( Liz is my 8 yr old daughter, gina is my 8 year old niece). I'm like ok cute, so I turn the page and it said I love gina and she loves me. Ok that's nice.....then I turn the page and what I read literally shocked the hell out of me and I had to make sure I was reading it right. Please please please, do not be harsh, I am coming here for advice on what to do.

It said.. me and gina have sex....and it had a little drawing of them on top each other. I honestly felt sick to my stomach, I still am. And i don't know what to do. Or who to go to about this. I'm only 25. My daughter was touched on the butt once by my boy cousin( he was over visiting one day, I walk to the kitchen for two seconds come back to the living room and cought him) and called the cops. I talked to my daughter about it and she said she was fine. My kids are always with me always and if not, I know who they are by, what kind of people visit them when my kids are by them. I never not know what they are doing. I'm like this because I was raped at 6 years old, and abused till I was 10. I trust no one!! now I see this and idk what to think! When I'm at my brother's they play together, outside or in the play room and I didn't think I have to be worried. My brother has shared custody of his two daughters. There mother is a good mom, but is constantly with different men. I don't want to blame everything on my niece but. Idk. My brother says Lina acts out, doesn't like to bath and wets the bed still, signs to me that sound like somethings been happening to her, but no one listens to me. How do I telly brother what I found. How do I talk to my daughter about this. I never told anyone about what happened to me, no one talked to me about these kind of things. I don't know what to do.