The actress that plays cousin Sally Ponting is Jillie Mack, a stage actress and eventual wife of Tom Selleck. They were married in 1987.
The title is a reference to the character Professor Henry Higgins from George Bernard Shaw's play Pygmalion and the Lerner and Loewe musical adaption My Fair Lady (1964).
This is Jillie Mack's second appearance in the series. She first appeared in an uncredited role (English girl at party) in Season 4 "Rembrandt's Girl" (1984).