Luka finished second in 800m with a timing of 2:01.75, which is her best effort of the season. She missed London Olympics qualifying 'B' standard of 2:01.30 by less than half a second.
America's Latavia Thomas won gold, clocking 2:01.57 while Canada's Bekkeau Karine won bronze with an effort of 2:02.54.
Luka, who holds the national record of 1:59.17, had won gold at Karlstad in Sweden in 2:02.58 and at Amsterdam in 2.03.62 last week.
She has already qualified for the World Championships to be held at Daegu, South Korea from August 27 to September 4.
In the men's 800m run, Ghamanda Ram also finished second with a timing of 1:47.50, which was better than the effort of 1.48.84, which fetched him a silver at Amsterdam.
The World Championships and London Olympics 'B' qualifying standard for men's 800m race is 1:46.30.
Luka settles for silver at Flenders Cup
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