Through the Nethergate - Roberta Eaton Cheadle - Bog

Margaret, a girl born with second sight, has the unique ability to bring ghosts trapped between Heaven and Hell back to life. When her parents die suddenly, she goes to live with her beloved grandfather, but the cellar of her grandfather's ancient inn is haunted by an evil spirit of its own.
In the town of Bungay, a black dog wanders the streets, enslaving the ghosts of those who have died unnatural deaths. When Margaret arrives, these phantoms congregate at the inn, hoping she can free them from the clutches of Hugh Bigod, the 12th century ghost who has drawn them away from Heaven's White Light in his canine guise.
With the help of her grandfather and the spirits she has befriended, Margaret sets out to defeat Hugh Bigod, only to discover he wants to use her for his own ends - to take over Hell itself.