Despite being played in almost every position during her early career, by 2011 Cullen had become more accustomed to playing as a defender. The Northern Mystics featured a strengthened lineup for their 2011 campaign, adding former Australian representative player
Megan Dehn in their attack end, and former Silver Fern
Anna Scarlett in the defence circle. The Mystics started their 2011 season well, including an early upset win over 2009 premiers the
Melbourne Vixens. Cullen's mobility and athleticism featured in a makeshift defence lineup following injuries to key defenders. Cullen played in all of the Mystics' ANZ Championship games in 2011. The Mystics finished the round-robin season in fourth place, scraping into the finals series. Standout performances against the New South Wales Swifts and Waikato Bay of Plenty Magic earned the Auckland franchise their first ANZ Championship grand final appearance. Despite her young age, Cullen was picked in the Mystics starting lineup at GD for the grand final against the unbeaten
Queensland Firebirds, matching up against experienced Australian GA
Natalie Medhurst. After a closely fought first half in the grand final, the Firebirds gathered momentum to secure a comfortable 57–44 victory. Cullen was rested in the third quarter of the match, during which the Mystics defenders struggled to keep up with the Firebirds' attacking pace. After a stellar 2011 season with the Mystics, Cullen was named as the competition's Best Young Player. She was also selected for the inaugural ANZ Championship All-Star Team, slotting in at wing defence; fellow Mystics defender Anna Scarlett was named at goal defence. Following her stellar ANZ Championship season, Cullen joined the New Zealand U21 team in a three-match series against Australia U21, which New Zealand lost 2–1. ==The Silver Ferns==