Matron Ji had eaten the Imperial Kitchen's food. Though it was common knowledge that the food sent tends to be spoiled or not too fresh, they had never caused such a severe reaction before.
Even I had eaten some of the vegetable dishes they provided, though I did toss them back on the wok to cook them once more.
Matron Ji had eaten the food that the Imperial Bureau had sent in the afternoon. She thought that the tofu smelled a little weird, but she ate it without much thought. We didn't have much in the first place, and of course, the best items had to go to the Prince.
There was no way to test if the food was genuinely poisoned, since Matron Ji had finished the entire thing. But everyone could tell Prince Zheng's anger, which caused everyone to keep their heads down as they worked in the Palace.