Who is Grandma Redbird from Betrayed: A House of Night Novel and what is their importance?

Grandma Redbird is Zoey's grandmother. She is of Cherokee Indian descent, and it seems as if she is also a vampyre. Grandma is very supportive of Zoey studying at the House of Night. Zoey believes it is her Grandma's support that has kept her sane since her mother married John.