Why does Melinda refer to herself as a ''wounded zebra''?

It's Melinda's first day at high school. One thing we already know about her is how incredibly isolated and lonely she is. On her way to school, she was the only one on the bus who sat alone. This pretty much sets the scene for how she'll behave when she gets to school. Along with all the other ninth-graders she's herded into the auditorium for student orientation. Melinda looks around, making note of all the various high school clans. She doesn't fit into any of them.
Rachel, her ex-best friend, mouths the words "I hate you." Melinda tries to deal with the insult by biting her lip until it bleeds. Then:

I stand in the center aisle of the auditorium, a wounded zebra in a National Geographical special.

Melinda uses this metaphor to highlight just how lonely and vulnerable she feels at that specific moment. If you've ever seen a National Geographic wildlife special, you'll know that zebras often become separated from the herd by lions and other predators, which then makes it easier for them to attack and kill. Melinda doesn't have a herd to belong to, and she's surrounded on all sides by predators. One of these is Mr. Neck, a teacher, who rudely tells her to sit down.
After she does as she's told, Melinda notices another "wounded zebra" smiling at her. She introduces herself as Heather from Ohio. But there's no time for a chat. The lights go down and it's time for student orientation, or as Melinda calls it "The First Ten Lies They Tell You In High School."