Okay. This collab will probably raise some questions about Boss. If I explain it out right, there will be a lot of confusion for any who haven't watched Angel Beats and given the interpretation of the Beats universe being made, it might still be confusing regardless. 

Most of it is just as Boss said, there are other places like the school that everyone is in that work for others who don't fit Angel Beats' criteria. She worked her way through one of them and ended up "upgrading" to this one.

Or if you prefer:

Boss was a criminal. And God brought her back. The End