From These Are The Voyages: TOS, Season 1 by Marc Cushman with Susan Osborn:
Roddenberry wrote to [Sam] Peeples suggesting many changes and specifically asking that Dehner be portrayed as ‘something less than a ‘swinger,'” that she be “a little overly intelligent and inhibited.”
NBC’s Donald Bays wrote to Roddenberry after reading an early script where Gary Mitchell refers to Dehner as “frigid,” saying:
The sexual connotation of the word “frigid” precludes its use with reference to Elizabeth. It is suggested that another word conveying her chilly exterior be found.
The substitution? “Walking refrigerator unit.”