Zelda is an evil sorceress and the main antagonist of The Swan Princess 3: The Mystery of the Enchanted Treasure. She has a magic wand that can send out a seeker, usually to bring someone to her.
After Rothbart lost his power and was banished, Zelda found him and helped him regain his power. She wanted to rule by his side, but he instead planned to force Odette to marry him, rejecting her in a similar manner to Clavius.
After the deaths of Rothbart and Clavius and the destruction of the orb that contained the power of the Forbidden Arts, Zelda captured a yakkey bird named Whizzer and forced him to be her spy, instructing him to find out whether or not the notes to the Forbidden Arts still existed. Whizzer found out that Derek and Rogers kept them around.
Zelda infiltrated the castle by pretending to fall in love with Rogers. She found the room with the notes and took them. However, though the notes on the power to create and the power to change were still intact, the last word of the notes of the power to destroy - the power Zelda wanted most - was torn off by Derek. So Zelda kidnapped Odette (taking Jean-Bob with her as well) using one of her seekers, demanding that Derek give her the missing section on the power to destroy.
Although she did not have the power to destroy, she did absorb the powers to create and change, during which Odette and Jean-Bob nearly escaped, so Zelda transformed Odette into a swan and trapped her and Jean-Bob in a dome of green fire that would instantly destroy anything that touched it.
Zelda transformed into Odette to ensure that Derek didn't try to trick her, and took the last word from him. Just as she absorbed the power to destroy, Derek was able to get Odette and Jean-Bob out of the trap. Then Derek fought Zelda, who sent a destroying seeker after Odette. Derek tried to break Zelda's wand, which would make the fireball disappear. Whizzer distracted her by imitating Rothbart's voice, and Derek grabbed her wand. They fought for a while before Derek finally snapped the wand in two, sending Zelda falling back onto her own trap, completely destroying her.
Unfortunately, Odette was already killed by the fireball, but came back to life when Derek destroyed the notes.