Catherine Lisa Bell (born August 14, 1968) is a British-American actress known for her role of Lieutenant Colonel Sarah MacKenzie of the television series "JAG" from 1997 to 2005, Denise Sherwood of the series Army Wives from 2007 to 2013, and Cassandra "Cassie" Nightingale of Hallmark's The Good Witch film and television series (2008–2015).