Zoey's our main gal in Marked, and this isn't just because all the action revolves around her—it's also because she's our first-person narrator, describing the stuff that happens to her and around her.
Because everything that happens in the book gets funneled to us from her perspective, we sometimes get a lot of gory details. For instance, when she's first Marked, we see her experience of it from the inside:
I sat up and coughed. I had a killer headache, and I rubbed at the spot right between my eyebrows. It stung as if a wasp had bit me and radiated pain down my eyes, all the way across my cheekbones. I felt like I might puke. (1.27)
Zoey spends a lot of time worrying that she might puke, and at one point in the book, she actually does. And guess what? We get front-row seats to it, because again, she's our first-person narrator, so we experience everything through her senses. Good times.
On the plus side, this narration choice helps us empathize with her (because all those huge life changes happening at once can be really hard), though on the downside it means we get treated to a ton of her anxieties, random thoughts, fears, and bodily experiences. Zoey's nothing if not an interesting gal to get to know from the inside, and by spending the whole book with her, we really get to appreciate how she changes as events unfold.