Her Sacrifice!
The Na Tribe's Sorcerer Holy Land was a hallowed ground where only the current Witch Queen and her successors knew the location. This land was the tribe's ultimate legacy; inside contained the Sorcerer's mysterious power. Foreigners were not allowed to enter. Otherwise, that would defile the land of the Sorcerer and blaspheme his name.
Although her tribe had already perished, Na Yi would rather die to maintain the long-gone glory of her people. But now, her younger sister had fallen into the hands of these two beasts, and thinking of the tragically pitiful fate that would befall her little sister was like a sizzling knife that pierced Na Yi's heart. She could do nothing but repeatedly delay her compromise to protect her.
The monkey-faced man had found out that Na Yi was intentionally delaying, so he had given her a warning earlier.