The 21-year-old hammer thrower, who reached the Olympic final in London last summer with a British record of 71.98m before finishing 12th, ranked tenth in Spain with a best of 66.69m.
Hitchon produced the distance with her final throw in Castellon with Zalina Marghieva of Moldova taking victory after a throw of 71.98m with her very first attempt.
Meanwhile fellow Brit Rachel Wallader placed 12th in the shot put with a distance of 15.20m with Olympic and recent European indoor silver medallist Yevgeniya Kolodko the winner with 19.04m.
Mark Dry won the B competition of the men's hammer with a season's best of 73.22m while British teammate Alex Smith, who beat him to a place at the London 2012 Olympics, was third with 68.34m.
Sarah Holt also placed third in the B competition of the women's hammer after a best throw of 65.82m while Sophie McKinna was second in the under-23 shot put event.
McKinna recorded a best throw of 16.09m as Emel Dereli of Turkey took victory with 16.78m while Joe Dunderdale placed sixth in the under-23 javelin event with a season's best of 73.02m.