What better way to feel like a princess than to actually dress up as a princess?
I think you would be a very cute Snow White - http://www.cardboardcutouts.com/0638%20Snow%20White.jpg
Perhaps Princess Millerna from Visions of Escaflowne? - http://www.rubberslug.com/user/f88a4...0(ep%2022).jpg
Maybe a character from one of the most famous romance anime of all time, Ah My Goddess? Urd - http://4.bp.blogspot.com/_z5R8mw_J0d...urd-megami.gif
How about a Mario Brothers Princess? I think Princess Daisy would fit the bill - http://thegamereviews.com/userfiles/...omen/daisy.PNG
If it's Sailor Moon you want, I think you would be a good Black Lady
A lot of girls like wearing wedding dresses. Perhaps Salvia from Wedding Peach? - http://thumbs2.modthesims.info/img/6...4_untitled.JPG
Ultimately, it depends on what you would consider to be "girly". Girly characters might act girly, dress girly, or just be from a girly show.
Hope I at least helped get the brainstorming started!