Galadriel is a modern mythical figure, who inherited from Circée and Cassandra.
Circée is a character of the Odyssey. She is a magician who works with drugs, in the story she lives in Aïa island. (With Médée, she is the only wizard in the greek mythology). She turns the Ulysses (or Odysseus) sailors into pigs. But she falls in love about Odysseus, so she gives backs their original appearence to the sailors. So she is good and bad at the same time.
Cassandra is a princess of Troy. In exchange of the power of being an oracle, the deus Apollon wants to seduced her. At the last momment, she refuses. So to avenge himself, he gives her a spell: she will have the oracle power, but no one will never believe her. So before the fall of Troy, she sees the future, and the tragedy occurs.
Galadriel, the elfic witch in the lord of the rings, was created by Tolkien, but she inherits a lot fom greek mythology.She is described like a witch who was good but with an obscure part, like Circée in the Odyssey. Moreover she's got a magic object: a fountain wich could be a mirror of future. So like Cassandra, she's an oracle, she can have visions in water. When Frodo meets her in the book, she tells him: "The mirror shows thigs that happened, things that are, things that should be", and after Frodo has got a vision of the devil Soron's eye. So we can see that often Modern mythology finds her roots in Antic mythology.