Who is Rachel from Wizard's First Rule and what is their importance?

A very young orphan girl of about eight years, Rachel lives in the castle of Queen Milena where she is the playmate of Princess Violet. Her existence is miserable. She wears raggedy clothes, is seldom fed and has no shoes. Princess Violet hacks Rachel's hair off in jagged pieces and slaps her for pure meanness. At night Rachel sleeps in a locked box in Princess Violet's room if she is lucky. If she has offended the Princess in any way, she is forced to sleep outside in the forest, alone, even in the middle of winter.