Who is Mabh from Wondrous Strange and what is their importance?

Mabh is one of the queens of the Otherworld. She is punished to confinement when she gives her mortal boyfriend, Herne, an enchanted gift. The enchanted gift is a roan horse. The roan horse turns its ride, and in this case Herne, into a hunter that will only hunt the most cunning of prey, which turns out to be people. Mabh is also Kelley's biological mother.