Minnie Taur is a 2011-introduced and fiction-only character. She is the daughter of the minotaur and probably a student at Monster High. She is also only a mention-only character, as her appearance or looks are not given anywhere in the franchise.
Minnie is the sister of Manny, though it's not known whether she is younger or older. Manny fears her knowing of his bullying, but whether that is because he's afraid of her or for her is unclear. She has an uncle who owns a rock quarry.
While they probably aren't friends, she and Frankie do know each other.