Jem, A Foreigner in Philadelphia by Delaney Green

From Delaney Green:

Philadelphia, Pennsylvania, thirteen years before the Revolution.
Apprentice physician Jem Connolly sets sail for the New World to escape Patch—an agent for a Dark power that wants to drain Jem’s inherited magic, Second Sight—and to fulfill the prophecy of her mentor in magic, Granny Kestrel, that Jem will find her destiny in America. In London, 14-year-old Jem studied with Ben Franklin; in the Colonies, Jem will stay with his wife, Deborah, and their daughter, Sally. When Jem's ship lands in Philadelphia, she expects to find out right away what she’s supposed to do with her life. Instead, she clashes with a rude frontiersman, doctors the crew aboard a quarantined plague ship, battles a practitioner of voudon, and meets a mystic who takes her on a journey into a world that shimmers beneath our own, a world that connects to Jem’s visions. Jem wants to find her destiny—but where is she supposed to look?