Are the parentheses in her response necessary? Also, I think that ma tag to be a possible mistake so I'll remove it.
They are, because there's a type of wordplay going on that doesn't translate well to English. The kana next to the kanji are usually used to show how they're meant to be read, but here they're being used to communicate two messages at once. What she actually means is she's the pupil, but all she really "says" is "Yes", with the part about the pupil being "hidden" in the text. It's a joke aimed at the reader.
They are, because there's a type of wordplay going on that doesn't translate well to English. The kana next to the kanji are usually used to show how they're meant to be read, but here they're being used to communicate two messages at once. What she actually means is she's the pupil, but all she really "says" is "Yes", with the part about the pupil being "hidden" in the text. It's a joke aimed at the reader.