According to T. Ray, what was Lily's mother doing on the day she died?

The day before Lily starts first grade, T. Ray confronts Lily about what happened to Deborah. He says she was cleaning out the closet, and T. Ray is shocked when Lily confesses that she remembers. T. Ray says that after she picked up the gun, it just went off, killing her mother. He adds that Lily did not mean to do it, so now she knows what happened.