What objects could represent Firegirl?

1. The first object in the story that might represent Firegirl, or Jessica, is the broken prayer ring. Look in Chapter 9, where Jessica is present at school for the first time at St. Catherine's when the kids are supposed to form a circle, hold hands, and say a prayer. Although Tom, the narrator, manages to hold Jessica's hand on one side, Jeff is on her other side and refuses. (He's the less sensitive of the two boys, easily grossed out, and only interested in Jessica to satisfy his own morbid curiosity.) 

A prayer ring is supposed to be a symbol of unity, but when Jeff won't complete the circle by holding Jessica's burned hand, the circle is broken and now represents a lack of unity: a failure for the kids to make a connection, both literally in the prayer circle and figuratively by developing friendships with Jessica. Therefore, the broken prayer ring, by being damaged and incomplete, represents Jessica at the beginning of the story.

(Whoever designed the cover art for my copy of Firegirl must have thought the broken prayer ring was an important symbol, too. The cover has an image of paper children all connected, except for a gap in the middle where a burnt paper child is only holding hands with the child to her right and not to her left.)

2. The photograph of "Anne" is a representation of both Jessica's past and of what Jessica longs to be. We see this item as Jessica accidentally drops it from her pencil case in Chapter 11. Anne is supposedly Jessica's sister who, we assume at this point, died in the fire that injured Jessica so badly. Because we see "Anne" smiling beautifully, looking happy, and playing tennis in the photo, and because Jessica carries it around with her wherever she goes, we can interpret the photo as a symbol of everything Jessica has lost and everything she wishes she could get back, namely, her own normal self. So it makes sense in Chapter 14 when we find out from Jessica's dad that there never was an Anne. It's a photo of Jessica before the fire.

3. Jessica's open bedroom window represents her longing for escape from her situation. By Chapter 13, we know that she feels trapped inside her damaged body and trapped inside her home with a mom she hates. But she likes to leave her window open, for the fresh air and the possibility of escape that it brings:

"...it feels like I could glide right out over the yard. Not fly really, but just sort of swim in the air. Slow."

"The wind goes through the leaves in the trees and I feel like I could move out into it."

Thankfully, her new and tentative friendship with Tom helps ease Jessica's sense of isolation and unhappiness. You might liken him to the breeze that rolls into her window.