When an atractive female thinks she is far more beautiful than all other women around her. Because of this she thinks she deserves to be treated superiorly, and makes demands on those around her. Her attitude is very centered on herself, but she suffers from very low self-esteem in actuality. Women suffering from pretty girl syndrome are often treated badly by the men they care about the most.
Frank meet Sally & Suzy at the club at the very same night. Because of Sally's pretty girl syndrome she was upset & shocked when frank was interested in Suzy and not her.