Indeed she is. Sheila didn't want the balloon she was offered so Maddie behind her took it because Maddie is so nice and want's to avoid conflict. Sheila was ready to tear few human throats but some of the other penguins managed to stop her. George the historian wrote that few compromises were made between human and penguins but at some point Sheila referred to those historical documents as ass wipe papers that are not even good enough to wrap the dead baby penguins that will drown because of all the melted ice. George is somewhere far back in the line because he fears the wrath of Sheila so much. So Sheila is, after all the kilometres they've already walked back, still very much pissed.