The story
A literary invention, first appeared in the Swedish novel Kyrkoinvigningen i Hammarby (1840-1841) by Emilie Flygare-Carlén, translated into English as "The Magic Goblet" (1845). Similar names of ambiguous origin, Elma, Selma, Velma, appeared in the 19th century. By folk etymology explained as Ancient Greek θέλημα (thélēma, “will”). Notice also the Spanish and Portuguese Telma, a rare feminine form of Telmo, ultimately from Santelmo or Saint Elmo.
Etymology from Wiktionary, CC BY-SA 4.0.