Aunt
From wipipedia.org

An aunt is a female relative; she may be a blood relative, i.e. the sister of one's mother or father, or an in-law, i.e. the wife of the brother of one's mother or father. The term is sometimes used loosely for a more distant female relative or a close family friend.
Aunts are favourite characters in spanking, feminisation or female domination scenes, usually in the role of a mature spanker or domina.