She was in the Library, among the survivors. But she also watched the Prince of Hell at the entrance to the Library from a window in Town Hall, and she followed the girl in the dark alleyways. A multiplicity of states happening at the same time which collapsed into a single state when observed. But that was the point. She wasn’t being observed.
The Horsemen couldn’t feel her, either. They were oblivious to her, completely unknowing of her presence, unsuspecting, thinking that the monsters were those who had recently appeared in town, promising to bring the end to it all. They didn’t know that the monster had been conjured into Fiery Creek long ago, residing there for a long time, feeding on her neighbours’ misery.