Maguire, who shared 10th spot after Saturday's third round, still had the consolation of winning the Smyth Salver for finishing top amateur.
The 21-year-old Cavan woman's next event will be when she represents Ireland at the Olympics in Rio.
Thailand's Ariya Jutanugarn earned a three-shot victory at Woburn.
Jutanugarn regrouped from a back nine wobble as she double bogeyed the 13th to finish three ahead of her playing partner, South Korean Lee Mirim.
Irish amateur Leona Maguire lost ground on the final round of the Women's British Open at Woburn as a closing 75 left her in a share of 25th place.