Anyone know of a website where i can get a FREE background check?.. ?

I'm trying to find out more info on a crazy girl who has wedged her way into my brothers life.. she is so strange and I'm the only one that see's it. I saw her put a pill in my brothers wine, when I asked what it was she said his vitamins so I said to my brother as he was about to drink his wine "why do you out vitamins in your wine?" He had no idea she did t and when I told him she just denied it. She also lied and said she worked at a law office that my ex boyfriend happens to still work at.. anyways when I told my bother **** these things and a few other weird things he didn't believe me and my mom told me to stop making things up! What should I do, I think she's trying to harm my brother. She even listened to him tell a story about how he had an allergic reaction to almonds.. the nxt day she showed up with cookies that had almonds in then and failed to mention it to my brother and then she was all apologetic like she didn't know. Everyone told her "oh its ok you didn't know ".. when said HELLO!! She was informed yesterday my bro didn't remember telling her. What should I do?