It was Couch’s fourth individual medal from six finals.
Couch, showing all her experience on the outdoor boards in windy conditions, had been on course for silver in Mexico with all her divers scoring more than 71 points.
She was second all the way through the final but was overtaken on the very last dive by Chinese teenage sensation Quian Ren, who finished just one-and-a-half points ahead of the Plymouth diver.
China’s Yajie Si won the event with a score of 392.50, with Ren collecting 372.15 and Couch 370.60, which was just one point off her personal best.
Canada’s Roseline Filion, who was Couch’s main challenger for the overall title, finished fourth with 344.26.
Couch ended up winning the overall World Series title by an incredible six points.
Her Plymouth and Great Britain team-mate Sarah Barrow missed out on the final in Merida.
Meanwhile, Tom Daley won bronze in the men’s individual final in Mexico. It was his second third place of the three-day event in Merida, having won a medal in the mixed three-metre synchro final with Alicia Blagg.
Daley 545.65 points to finish behind China’s Jian Yang (570.05) and Mexico’s Ivan Garcia (555.80).
Plymouth-born Daley finished second overall in the six-leg series behind Yang.
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