Books in the Eternal Spring, Invisible Forest series

She has a tail. Normal is relative.Kellan is a shape-shifter and a member of a secret society, the Sankhain, who protect a fountain of youth hidden in an invisible forest outside Madison, Wisconsin. When a stranger asks Kellan for her help with some documents, documents which shouldn't exist, about the Sankhain, Kellan uses her unique sense of smell to follow the trail, which leads to the very heart of the Sankhain. What Kellan uncovers will shake her world to its core.