Melior is a Cornish and Devon girls name, sometimes spelled Meliora. This was the name of a fairy in medieval legend, sister to the illusive Melusine, except all we really know about her is that she lived on the Isle of Avalon. Her story can be found in Jean d'Arras's Le Roman de Melusine, where Melior and her sisters take revenge upon their father for breaking their mother's marriage terms, but their mother punishes them for the act. Melior's fate was to be imprisoned in an Armenian castle. In The Romans of Partenay, the king of Armenia completes a challenge and asks for Melior's hand in marriage, but Melior knows that he is a descendant of her sister Melusine. He doesn't really care, but they still don't get married. Their sister Palatine has no better luck, as she was punished to guard a treasure that no man can win.
There's another namesake, however - Saint Melior, whose gender is undetermined. If someone wanted Melior for a boy and Meliora for a girl, or Melior for a girl, I don't think it would cause any fuss. The name likely comes from Meleri, a form of the Welsh name Eleri, probably meaning "earth, soil." A different chain could make Meliora come from Latin melior, meaning "better." Meleri and Eleri have their own historical namesakes: Eleri, daughter of Brychan Brycheiniog, and Meleri, wife of the legendary Cunedda. However, there is a chance this name is actually connected to the male name Meilyr from Old Welsh, which means "May sea." This was the name of a 12th century poet, and variations on the name include Mylor and Meilir. Melora is a variant of Meliora.
For a rare name from a small country, there are still a couple namesakes. In literature, Melliora is a character in Eliza Haywood's novel Love in Excess, and in Victoria Holt's novel The Legend of the Seventh Virgin, although it is spelled Mellyora there.