Monteiro showed much improvement in the 2008 season. She ran her fastest ever time at the World Cross Country Championships (27:12) and took fifth place at the Rotterdam Marathon – her first competitive outing over the distance. She qualified to represent Portugal at the 2008 Beijing Olympics but she did not manage to finish the Olympic marathon race. She closed the year on a positive note, however, winning the Ovar Half Marathon for a fourth time, and taking individual bronze and team gold at the 2008 European Cross Country Championships. She closed the season by beating Olympic silver medallist Eunice Jepkorir to win the Cross Internacional de Venta de Baños.