That's why I said "some variation."It doesn't have play on the fact that he's a talking animal so much as the fact that his life is expendable to her vis a vis he's a bad guy who Marcy has a quest to kill.
Also I would not be so sure Marcy values the lives of the Amphibians intrinsically. In some of her first lines, Marcy likens herself to a DnD player character and a video game protagonist who does quests and levels up. One of the first things she does to the Plantars is to put them in a trope box. She does save Sprig, but she was also very clear that that action girl routine put her in no danger. By her own admission she wasn't risking her life in there.
Marcy values the King, and Lady Olivia. She likes Anne and the Plantars. But I don't think that extends to every talking critter in Amphibia. I can definitely see that video game mentality they hammered home in her intro meaning that she has no qualms about killing someone.