As a high school student, Cullen played representative netball and basketball, and competed at a national level in athletics.

She attended Auckland Girls' Grammar School, during which time she competed at national level in athletics, and represented New Zealand in basketball and netball.

[5][6] With her family struggling to raise funds for Cullen to represent New Zealand in two sports, she was donated money to participate in the NZSS netball team's tour of Australia that year.

[8] NZSS defeated Australia in the final of a regional secondary schools tournament held in Auckland in June that year.

[9] Cullen's recovery and NZSS performance led to her being recalled into the New Zealand U21 side for the 2009 World Youth Netball Championships in the Cook Islands, subject to medical clearance following her ACL injury in 2008.

[16] Coach Robyn Broughton opted to use more experienced players for most games, although Cullen was trialled in different court positions, even playing at centre.

[17] After struggling through the round-robin matches, the young New Zealand side went on to win the 2010 title, defeating hosts England 28–26 in the final.

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.

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.

[24] With injuries to two of the incumbent defenders in the national team, Cullen was named in the ferns for the end of 2011 series against England and Australia.