She thinks of the demon from the sun. It's very possible.

She smirks faintly, and recites the poem, an obvious choice but still somewhat appropriate: "Some say the world will end in fire, some say in ice."

Her eyes are still challenging, baiting, almost teasing; she knows where the poem leads as well as he likely does.

Or view it another way: Having destroyed Princess Snow Kaguya, who'd wanted to cover Earth in ice, will they face Fire next?