Sister Finland is a minor character in the comic. Like her brother Finland, she is homely, grouchy, uncommunicative (never having spoken a word in the comic, she may be literally mute), and hard-drinking.
She functions as yet another complication in the Sweden-Finland-Åland drama, since not only does she have a fierce crush on Sweden, but she has a child (FennoSwede) by him as a result of a drunken fling back when he was still trying to be straight. Thus she considers Sweden to be rightfully hers on the basis of first come, first served. His own feelings on the matter don't really enter into it, but for all her grimness and violent tendencies, she is a doting mother.