Cullen's father was a golfer and her mother played professional squash. She first played hockey aged nine, when living in Kenya until she was twelve. Her parents still live in Kenya where they run the Hemingways hotel near Watamu. She boarded at the independent Oakham School in Rutland. She then studied for a BA in Business Studies (Strategy & Entrepreneurship) at the Nottingham Business School, gaining a 2.1 in 2006. She works as a Business Development Consultant for The Kennel Club. Her brother Gray Cullen played junior rugby for England and in 2009 debuted for the Kenya national rugby union team.