She was the woman that Jerry met in the Super Market. After meeting her, he tells George that he can't remember her name. He attempts to get it from her, but the clue he can get is it rhyms with a female body part.  She finds out that he doesn't remember, gets pissed, leaves.  He then remembers as she leaves, yelling out the window "Deloris!!!!"

Although he remembered her name, the credits still identify that character as Mystery Woman.