The German rider took home the lion's share of the €106.500 purse riding Gangster Montdésir in the field of 40 over Grégory Bodo's course.
The reigning European champion from Belgium rode Zonik Plus to a personal best score of 81.195%, well ahead of Becky Moody and Jagerbomb.
The German and the 14-year-old bay gelding won the FEI Dressage World Cup Grand Prix - her sixth victory at this French venue.
Just days after making assurances that the international horse show would proceed, organizers have had to pull the plug because of France's 9 p.m. curfew.
The Longines Equita Lyon, Concours Hippique International has been reconfigured and will be held with a maximum of 1,000 spectators.