Nathalie did make some mistakes - although so did most of the other riders. Dressage is one of the sports where not making mistakes is virtually impossible.
She finished 12th overall, with a score of 79.089 and had actually improved since the Team Dressage (back then, her score was 75.857).
Overall, I thought she performed pretty well. No chances of a medal or even a Top 5 finish because those riders showed exceptional riding. Charlotte Dujardin from Britain won with 90.089 points (which is, if I'm not mistaken one of the highest scores in Individual Dressage in many years), followed by Adelinde Cornelissen from the Netherlands with a score of 88.196 and Laura Bechtolsheimer, also from Britain, with a score of 84.334.