Cockburn and her partner, Rosannagh MacLennan, were ranked first in Women's Synchronised Trampoline following their two winning performances in 2007.

After winning the Canadian National Trampoline Championships seven years in a row, Cockburn made an error in her second routine (of three) and came in 6th place in the 2005 finals on June 1, 2005.

In the 2006 Canadian National Trampoline championships in Quebec City, Cockburn regained her title beating MacLennan into second place, on May 20, 2006.

On June 7, 2008, Cockburn won her 10th Senior Women's Trampoline Canadian Championship in Calgary, beating MacLennan into second place.

In 2011, Cockburn did not compete in the Canadian National Championships and was sick for the Finals of the 2011 Pan American Games.

In the 2011 Trampoline World Championships in Birmingham, England, Cockburn and MacLennan secured two places for Canadian women in the 2012 Summer Olympics and Cockburn won a Silver medal for the synchronised trampoline event (with MacLennan) and a Bronze medal for the Team competition.

[7] While training at the Trampoline World Championships in Daytona Beach, Florida, in November 2014, she landed badly and broke her ankle forcing her to withdraw from the competition.

[8] Cockburn received the honour of being selected to pronounce the athletes' oath in front of her home crowd in Toronto during the opening ceremonies of the 2015 Pan-American Games.

On July 16, 2017, at the 2017 Canadian National Trampoline and Tumbling Championships, Karen Cockburn officially retired at a ceremony held to honour her contribution to the sport.