Rostkowska made her official debut for the 2008 Summer Olympics in Beijing, where she competed in the women's 800 metres. She ran in the first heat of the event, against six other athletes, including Russia's Svetlana Klyuka, who nearly missed out of the medal podium in the final. She came only in third place by five hundredths of a second (0.05) ahead of Great Britain's Jemma Simpson, with a time of 2:02.11. Rostkowska advanced into the next round of the competition, as she secured the final mandatory qualifying slot in the first heat. Rostkowska, however, fell short in her bid for the final, as she placed fifth in the second heat of the semifinal rounds, with a time of 1:58.84.