>>3992817
Amir said that she had basically proven that her intentions were genuine. So possibly not something she explicitly did or said to Alastor, but he knows that she won't double-cross him like most of the other people in Hell. Plus there's still the favour she owes him, I think Alastor would be pleased that he has even that small amount of leverage over Charlie even if he hasn't exactly planned what to use the favour for yet.