There isn't really much context to the word コピー here, so I am inserting the whole page of the manga. I understand the basic meanings of コピー, which are pretty much the same as the English copy, but I have no idea how to translate it here. The screaming girl is Yozora. Her older sister is held back a grade and they will both end up in the same grade next year. I think コピー refers to the phrase 姉と同級生なんて嫌だ。 Yozora hasn't used the phrase before, nor has any other character. Do you have any idea what コピー might mean here?
Edit: The name of the manga is 僕は友達が少ない volume 19 (English title: Haganai I have few friends). Based on a light novel by Yomi Hirasaka 平坂読. Manga author: Itachi いたち. Art by Buriki ブリキ. Published by MFC MFコミックス, Kadokawa.