Galadriel is a central character in the Tolkien Universe and she’s been around since the First Age. That’s the reason why she was chosen to begin the Mithril range. Though being the first released reference, this figurine is not as rare as one could think.
“Yet more fair is the living land of Lórien, and the Lady Galadriel is above all the jewels that lie beneath the earth” (LotR, Book II, Chapter 7 : “The Mirror of Galadriel”)