A revenge story of a 12-year-old girl

Typically, a cop has around three informants, but this one has seven. She once gave me a document with a dedicated section for each informant. Some had committed crimes, some had turned traitor, and some had disappeared without a trace. I picked one, and the cop said, 'Alright, this informant is 12 years old.' This story revolves around a deadly gamble, and the 12-year-old 'informant' is one of the players. She must venture deeper into danger, step by step, closing in on the truth.