Van der Horst, who took double Gold at the 2014 FEI World Equestrian Games™ in France, sealed top spot in the Grade III Individual Championship on her bay mare Findsley.
Their score of 73.735% edged long-time leader Natasha Baker, of Great Britain, into second place as she excelled with new top horse Mount St John Diva Dannebrog, while American Rebecca Hart and El Corona Texel collected Bronze to become her country's first world Para-Dressage medalist.
"I am really thrilled," Van der Horst said. "It is so amazing to be world champion again. During my test, I didn't realize it was that good.
"I was just riding my test and doing what I do and it was not until afterwards that I realized it was good. In the beginning I was nervous, but I relaxed during the test and it got better and better. It's our first international competition together and I am so proud of her."
Baker, a mainstay of Britain's all-conquering Para-Dressage teams in recent years, was similarly delighted with the performance of her horse in what was a major championship debut for the partnership, as it had been for Van der Horst and Findsley.
"She was amazing, so, so, good and she went in there like she owned it," Baker said. "I am just so proud of everything that we have achieved in such a short space of time.