Belladoll knew Zarek well enough to know that he would do anything to protect Priya. Not only would he pull all the attention and danger onto himself, but after he heard of the Trial of Fire, he would almost certainly tie it to Crux and go out of his way to crush it before he left.
That meant that there was a trap waiting there almost certainly.
Zarek had already seen through it, which was why he had left her such a subtle warning. And yet he was running right toward it nonetheless.
That might even be why Belladoll had been so enraged. She said so wholeheartedly that she would enter the Trial of Fire, and while on the one hand Belladoll had just seen Zarek sacrifice himself in this way so easily, seeing Priya not hesitate to say that she would do the same moments later was like watching two people she wanted to get between grow closer.
It made her sick.