Like Darnell, Misty doesn't really have much going for her. We just know that she's a girl and that she survived in the tunnels with Mark and Trina and everyone else. For description, we get:
A girl walked in after him, tall and thin with long red hair, just a little younger than Mark. (2.33)
And, yeah. She dies from the Flare too. Yup; the minor characters drop like flies.