Yolanda evolved from the Spanish Violante, which is a very old name, borne by medieval princesses and queens but virtually disapeared nowadays. Also the most usual short name in Spanish is Yoli.
This name probably derives from another name, Iolanthe, which means "violet." The first part of this name, "Yo-" may come from "Io-," "-lan-" from "-lan-," and "-da" from "-the."