The polar opposite of Dane Cook's "The Karen"
Generally The Kathryn is the awesome girl at the party. She generally is able to show many people a good time in the least promiscuous way while keeping poise. Everyone at the party looks forward to the Kathryn showing up.
Person 1: This party is lame.
Person 2: Don't worry, the Kathryn of the party will be here any minute, things should pick up then!