Kuijken set a series of personal bests on the track in 2005: 2:06.25 minutes for the 800 metres, 4:19.72 minutes for the 1500 m (for seventh at the 2005 European Cup event), 9:28.45 minutes for the 3000 m (part of a silver medal win at the 2005 European Athletics Junior Championships) and 10:42.93 minutes for the 3000 metres steeplechase. On grass, she was a junior bronze medallist at the 2005 European Cross Country Championships and placed 58th at the junior race at the 2005 IAAF World Cross Country Championships.