Which person became a tenant by mistake?

The many pairs of tenants in "The Westing Game" all seem to have strong connections to Mr. Westing, especially considering they are all potential heirs to his multi-million dollar fortune. As they are going about their process of discovering his riddles and clues left behind, however, there is one character who seems to be a mistake—one who has little understandable connection to the late Mr. Westing.
Sydella Pulaski has a vague backstory and no connection to any of the other characters or Mr. Westing, making her mysterious and suspicious. She became a tenant apparently by mistake since she has no defined connection. In spite of her separation, though, she still takes kindly to Chris, and she participates willingly in the game.