Genes were the basis of every creature, on the most trivial level, cells made up the bodies of both humans and monsters, and to some extent they determined power. Sure, cells were just the foundation, but that was why they were so important.
Essentially anyone living in the Upper Ring knew this, perhaps except for the slums. All it took was a basic education and knowledge of biology - nothing complicated.
So, the girl wanted to alter her genes by eating too much monster meat in a short period. Technically, because of the amount of meat she consumed, her body began to consist of monster meat by a few percent.
Sure, the meat went into her stomach, but the first cells digested and had already reacted with the rest, then attacked the girl's cells.
If Adam had been in her place, he would have felt only a slight pain in the stomach area or no negative effects at all. However, this girl was a mere human.
