Thank you all for the contributions. It turns out that the author preferred a more literal translation ("machado de guerra") for Isabella Stone (Isabela Rocha). In her own words:
"... I lean toward the literal translation—Stone is feisty, forceful, overbearing, etc, but not a truly nasty person. This term is most often used to describe an authority figure such as a boss who is difficult, demanding, even temperamental--but not necessarily unfair or nasty."
https://pt.wikipedia.org/wiki/Machado_de_guerraIn other contexts, "megera" or "jararaca" might be applicable.