NO, more I worry is that chocolate is NOT for animals, especially cats and dogs.
dont worry she is a youkai this amount of chocolate is not enough to kill her and htat is if a youkai whoose form is mostly human is even affected i think that if they are capable of copying the human anatomy then they must be capable of copying the physiology and enzymes of a human
Chocolate and animals is partly because of their small bodies and low weight, IIRC.
Large sums of chocolate are poisonous to humans, we just require far larger sums to get to that point than a dog or cat. But Chen is, physically, the size of a young human, so her tolerance would be, at worst, between a cat and a human child, and at best would be equal or greater.