Joanna was a Scion of Erzulie, but was killed in a battle against some mysterious armed men when trying to save a student from the School of the Shining King in the town of Wonder Lake.
Book 2: The Missing Awakened Kids
Joanna was killed, but her strength of will was so strong that she became a ghost with a vow to save the Missing Awakened Kids, a group of awakened Scions that never got a Visitation or were rejected by their divine parents and are now being targeted by evil people and creatures.
Alexander Zhao and Balthasar Vonburen both can see her thanks to their Death Purview, and agreed to help her fulfill her vow. She acted as their guide in the investigation.