She enjoys studying, she truly does - more so than any of her siblings, probably. But here, in Narnia, there is a definite weight to all her actions, that if she fails at something not only will she suffer for it, but potentially the whole of their lands will be affected as well. It's something that she thinks is too much, at times.

"Oh Peter. You're the High King. Can you not decree a day that will free us from these responsibilities? Just... just for one day." And as she says this Susan is so horribly aware of just how childish she sounds.