Lady Marmalade was a 1970s French singer, who specialised in disco. Iris Wildthyme owned a tape by her. (PROSE: Enter Wildthyme)
Behind the scenes
In reality, Lady Marmalade isn't a singer, but the name of a song written by Bob Crewe and Kenny Nolan, first performed by the group Labelle. The wording about Lady Marmalade does make it appear that she is in fact a person within N-Space.