The Ivybridge Community College pupil was competing in the under-15 hexathlon competition.
Harris, who is in her first year at under-15 level, scored 3,285 points. Worksop’s Emily Rose won the national title with 3,565 points.
Devon champion Harris was ranked in the top four for the hurdles, long jump and javelin, but could not quite match that standard in the shot, high jump and 800m.
She ran 11.74 seconds the 75m hurdles, which was the third best time of the day. Harris’ 4.90m long jump was the fourth best leap, while her javelin throw of 23.66m was the second longest of the competition.
The Erme Valley Harrier was sixth in both the shot (8.53m) and 800m (2:34.64), but had to settle for eighth in the high jump with 1.50m.