Okay, So I'm a girl and i know some really good ideas for girls (or even girl friends) birthday parties. =)
1.) chocolate (may sound cliche.. but it's really sweet)
2.) A reeeaaalllyy large plushie of their fav animal. (cute)
3.) a CD of their fav music.
4.) a b-day date to the park. Ohh maybe a picnic! (maybe with some roses haha)
5.) (if the girl's a reader) A book or magazine
6.) Jewlery. maybe a heart necklace! Cute
7.) A box filled with diff. kinds of candies.
8.) Or you could just make her something.
write a description of her, but not anything 2.. u know, innapropriate. Make a card or poem for her. =)
9.) Tickets to a movie or concert. (just the two of u.. or a group of friends. ur choice)
10.) and if none of these work.. ask her friends! and tell them to keep it a secret!