I don't know. This strikes me as an introverted, creative kid who, as others have said, is getting her vocabulary from reading. Honestly--as long as she is happy I don't see anything wrong with it. Think of Anne of Green Gables. Other kids always think my dd12 is British because she enunciates and has a big vocabulary and loves words. She thinks that is funny. She has friends and is happy. I am not a big believer in conforming or dumbing down vocab. to fit in. Perhaps there is some kind of issue here, but I just don't see it.
http://www.amazon.com/Some-Best-Friends-Are-Books/dp/0910707960