The 18-year-old London Paralympian came second in the final of the Para Sport 100m breaststroke, clocking in at 1:25.15 to secure her place on the Australian team heading to Glasgow in July.
Downie, who has Scottish ancestry, said she was excited to see her grandparents when she heads over for the Games.
She also qualified for the 2014 Para Pan Pacific Championships in California in August.
During the six-day championships, Downie also won the Para Sport 200m individual medley in 2:35.66, finished fourth in both the multi-class 50m backstroke in 33.24 and the multi class 100m freestyle in 1:03.75, and came fifth in the multi-class 50m freestyle in 29.28.
Other local swimmers competing were Duncraig’s Rhys Mainstone, who finished fifth in the final of the men’s 1500m freestyle clocking 15:32.23, Sorrento’s Lennard Bremer, who came fifth in the men’s 200m breaststroke in 2:13.83 and 14th in the 100m breaststroke in 1:03.08, and Arena Swim Club member Yolane Kukla, of Marmion, who finished seventh in both the women’s 50m freestyle final (25.39) and 100m freestyle final (54.95).