Symbolism, Imagery, Allegory
Not sure about you, but when we think of fire, some of the first words that come to mind are burn and ouch and marshmallows. In "Spicy Little Curses Such As These," though, the fire we're dealing with isn't your ordinary fire; nope, it's Hell fire. Yikes, right? Not so fast: Just like the ocean is a normal part of Earth, fire is just a normal part of Hell. And like the ocean, Hell fire is actually an integral part of human life and rebirth. Souls go into the Fire (yes, it's capitalized in the book) when they die and are reborn into different bodies:
That was how it worked. The Fire took in souls and made them new, and Yama sleeved them into new bodies as he saw fit. Estella might be reborn as a tigress or a river dolphin or an ibex that could balance on tiptoe on a mountaintop. Or she might be born as a woman again… (2.11.9)
The Fire seems scary at first, but it actually represents the normal cycle of life and death. In a way, it's comforting for someone like Estella who's dealt with a lot of stuff in her life. It's nice to think that she'll just be reborn into a new life without any memories of this one. Her old life will burn away completely and she'll emerge anew.