Can someone explain me the Dionne Warwick-reference, please?

Dionne Warwick used to be commonly known in the 80's/90's as a late night infomercial "Psychic Friends Network" spokesperson/psychic.

There is a knock on the door and Bobby asks Ellen "who's that?" And she answers, "how should I know, I'm not Dionne Warwick", meaning, "I'm not psychic, let me physically go check like a normal person would do when answering a knock on the front door." I think it is meant to 'age' the movie appropriately, same as the clothes Ellen wears and the hairstyles. The movie was made I'm 2000, but is supposed to be set in 1990, hence the 80's/90's references.