Briana Cuoco. In "The Tangible Affection Proof", Briana Cuoco, the younger sister of Kaley, plays a former friend and new fiancee of Penny's former boyfriend. Penny is very jealous of Gretchen when she gets proposed to on Valentine's Day at the same restaurant where Penny, Leonard, Howard and Bernadette are having dinner. She is an actor, dancer, choreographer and has been a contestant on "The Voice"