She was a customer (played by Mitzi McCall) who has come to Katie's counter in the department store for some cosmetics. She asks Katie to put some make-up of the color "Summer Peach" on her face, but Katie tells her they do not have that any more and can only give her "Desert Dawn". The customer rebukes by saying that her skin has already got "desert" and reaffirms that she needs "peach". Katie just tells her not to screw with her.
This unnamed character appears on the original Unaired Pilot for The Big Bang Theory.