Cai Lin finished in a time of 8:54.64s, well outside the Commonwealth Games qualifying time of 8:45.38s and the Asia Games qualifying time of 8:33.55s.
The effort won her the gold medal for Selangor at the 57th Malaysian Open Swimming Championship, here Sunday.
Nadia Adrianna Redza of Selangor won the silver medal (9:09.41s) while the bronze medal went to Raina Saumi Grahan of Indonesia (9:12.51s).
"I am very disappointed because I failed to qualify for the 800m free style. I am tired because I went all out yesterday to meet the qualifying time for the 400 free style event but still failed.
"I still harbour hope to perform at the Commonwealth Games and Asia Games and will train very hard if the association (Malaysian Amateur Swimming Association) gives me a chance," she told reporters here, today.
The Commonwealth Games is scheduled to take place on July 23-Aug 3, while the Asian Games from Sept 19 to Oct 4.
Only Kevin Yeap, Daniel Bego, Welson Sim and Lim Ching Hwang had qualified for Commonwealth Games in the 4x200m free style relay event.
Meanwhile, another national swimmer, Yap Siew Hui of Selangor won a slot to the Nanjing Youth Olympic Games in the 100m butterfly stroke on Aug 16-28.
Siew Hui won the gold medal with the fastest time of 1:01.78s to surpass the qualifying time of 1:02.62s under category A.
The silver medal was won by Tang Jing E of Singapore (1:02.23s) while the bronze medal went to Monalisa Arieswaty of Indonesia (1:03.08s).