past mistress
/ˈpɑːs(t) ˌmɪstrɪs/ /ˈpas(t) ˌmɪstrɪs/noun
A woman who is especially adept or expert in a specified subject or activity. With in, of, at.
Origin
Mid 19th century; earliest use found in Mary Braddon (1835–1915), novelist. From past + mistress, after past master.