Mary MacDonald Kerr burst into the Milwaukee theater community in 1995 playing a young Armenian immigrant in the emotionally harrowing "Beast on the Moon." It was an auspicious debut in a local acting career that has become notable for its breadth and depth. MacDonald Kerr is especially adroit at finely tuned, sensitive roles. But what is the character that has stuck in the memories of Milwaukee theatergoers? It's Sylvia, a frisky and tirelessly ingratiating dog.