Art by A-KA
Translation by jokey665 on r/elsanna :
Elsa: “We could be Imoooooo~”
Elsa: “Imouto!!” (strangely written in katakana here, means younger sister)
Anna: “Elsa…”
Elsa: “Imooooo~”
Anna: “Those are the wrong lyrics…”
Elsa: “Imouto!” (written in kanji this time, still means younger sister)
Anna: “Are you doing that on purpose?”