Shelly is George Costanza's cousin, to whom she bears a strong resemblance. She appeared only once, in “The Contest”.
Biography
Not much is known about her, only that she is a cousin of George Costanza, and niece of Estelle and Frank Costanza. She visited her aunt Estelle in the hospital after falling after she caught George with a Glamour magazine. Shelly knows about George's writing job at NBC, as she had asked him about it during the visit, but he failed to answer due to the sponge bath of a female patient nearby.