Olympic silver medallist Samantha Murray won her first British Modern Pentathlon Championships crown in Solihull on Saturday.
Murray and Choong have secured places in the British team for the European Championships in Poland in July.
Murray, ranked third in the world, also won bronze at last year's World Championships.
Murray shot and ran strongly at the Tudor Grange Leisure Centre to finish 20 seconds clear of 17-year-old Eilidh Prise. Kate French finished third.
It meant Murray captured the senior and overall titles, with Aberdeen teenager Prise, a member of Pentathlon GB's World Class Podium Potential programme, impressing with the fastest run/shoot time of the day en route to the junior title.
The men's competition ended in a thrilling climax with five athletes in with a shout in the run/shoot.
It came down to a sprint finish, with 17-year-old Choong edging out Cooke, Britain's 2011 world junior champion. Joe Evans, bronze medallist on his World Cup debut in California in February, came home in third.