Ranked 396 in the world, the young German bested her better-known rivals in a jump-off to claim her first GP3* success - at the age of just 18.
New world number three Gerco Schröder and Carsten-Otto Nagel both retired but there was still plenty of quality in the field with the likes of Marcus Ehning, Christian Ahlmann and Luciana Diniz.
Kevin Staut, Lars Nieberg, Marc Houtzager and Albert Zoer were among those to qualify for the jump-off and when Herröder, on Pico's Boy, went off third and clocked 39.73 seconds, an upset did not seem on the cards.
Fellow German David Will blitzed round in 36.99secs, but with a fence down, he was bumped down to fifth place.
Only three riders managed to clear - Staut, Lars Nieberg and Sebastian Karshüning - but none of them could match Herröder, who claimed a famous win.
In the dressage competition, Austrian Victoria Max-Theurer registered victory with a score of 74.450 per cent in a Freestyle Grand Prix that featured just four competitors.