Beginning her club career with FH, Guðbjörg made 23 Úrvalsdeild appearances before signing for Valur in summer 2002. At Valur she overcame a series of injuries to claim four Úrvalsdeild winner's medals and one Icelandic Women's Cup winner's medal. She moved to Swedish Damallsvenskan club Djurgårdens IF Dam ahead of the 2009 season.
Guðbjörg (centre) playing for Djurgårdens in October 2012
Guðbjörg developed an affinity for Djurgårdens and was proud to captain the club. But several other players left due to economic downsizing and when the club was relegated in 2012 she had to leave to protect her national team place.
In early 2013 Guðbjörg moved to Norway to play for wealthy Toppserien newcomers Avaldsnes IL. She also had offers from clubs in Sweden, Germany and Russia.
After one season in Norway, Guðbjörg announced a move to the German club Turbine Potsdam in December 2013. She signed a contract to run for one and a half seasons from 1 January 2014, telling UEFA.com: "If one of the best teams in the world makes you an offer, you cannot say no."
National team coachSiggi Eyjólfsson selected Guðbjörg in the Iceland squad for UEFA Women's Euro 2013, while rival goalkeeper Þóra Björg Helgadóttir was recovering from a hamstring injury. Guðbjörg took the goalkeeping position at the final tournament, playing in all three group matches and the 4–0 quarter-final defeat to hosts Sweden. The Swedish press hailed her as one of the best players at the competition.