Zhang Liao's description gave Shen Hao a sense of "sugar-coated artillery shells." On the outside, it's fragrant candy, but inside, it's a deadly poison pill.
Following this logic, the next step would be for Qin Yurou, once she got the poison pill, to find a chance when Qin Xiuyuan wasn't paying attention, or make up some excuse, to pour out or destroy all the normal fragrant candies in his Purple Jade Bottle, leaving only the disguised poison pill inside.
The timing had to be just right. It should be completed shortly before Qin Xiuyuan's accident, so he wouldn't have time to refill new fragrant candies, and when he left the Qin Mansion for Prince Shou's Mansion, he'd take one as usual—and die.
This not only silenced him, but also successfully dragged Prince Shou into the mess. Two birds with one stone.
