Margaret Whitesell is a distant cousin of Dr. Brennan on her mother's side whom Brennan's father invited to spend Christmas with them in the episode "The Goop on the Girl."
Initially, Dr. Brennan dislikes Margaret, which Dr. Sweets would tell her is because Margaret's off-putting personality is too similar to Dr. Brennan's own antisocial difficulties. Booth notes a striking physical similarity between Dr. Brennan and Margaret, suggesting that they could easily pass for sisters (which the actresses are in real life). During Christmas dinner, Dr. Brennan finally expresses her irritation with Margaret's habit of quoting Benjamin Franklin, explaining that it is not really communication and that she would prefer to hear what Margaret has to say herself (without using Franklin as a proxy). Margaret replies, "That's the nicest thing anyone's ever said to me."