How did Princess Yin die?
There was no other reason; she died of illness. Human life can sometimes be incredibly fragile.
But if it had been someone else, they might not have died.
It was serious what she was hiding, and Princess Wuh saw it, which frightened her deeply.
Yet, no matter how scared she was, it wouldn't be enough to torment herself to death.
After Lady Li's servants were beaten, they naturally resented Princess Yin. Princess Yin had been out of favor for many years, while Lady Li had been favored for a long time.
Her servants, especially Zhao Fugui, were hardly ever punished. With just a few words from him, others would go through fire and water to accomplish tasks. He could kill Princess Yin without leaving any trace.
After some activity in the Imperial Kitchen, Princess Yin's days became very difficult.
Take her meals, for instance; how could a person who was so ill have an appetite for rich and greasy chicken, duck, fish, and meat?