My DD is turing 6 on Sunday!!! Depending on what your budget is with a 6 year old girl you can be safe with: Barbies, My Little Ponies, Littlest Pet Shop, Craft type things (markers, crayons, jewelry maker set), Hannah Montana, Zhu Zhu Pets....
We usually spend $20 - $40 on gifts for others birthdays that my DD goes too... I usually find GREAT deals on clearence items and have always had the gifts very well recv'd by the Child and the parent...
Have fun...