Emily, of course, had changed. She met me at the door as she met you. She was a shell burned out by one fierce moment of fire. The figurative language used in the excerpt is

The figurative language is a metaphor. That is because she didn't literally burn out by one fierce moment of fire, it's a metaphor to show the strong burst of emotions that she had at that moment that made her feel as if she was burning. It could mean either that she got angry or fell in love or anything similar.