Does she have a middle name? I don't think it's right to change a four year old's name, it would be different if she was like, a year old or something. She could always go by her middle name, or by a contrived nickname. (Like, if she's always happy, call her Smiley)
I have a friend named Karlton Bradley. When he was little they called him K.B. Now everyone calls him Kabe.
(Oh, and I saw your Eowyn post down the board. What is your daughter's first name? My fave combo is Winter Eowyn Eve)