HELP! Gift Ideas For a Girl Turning 18?

My Best Friend is turning 18 on the 29th and i still havent got her anything. i dont want it to be too expensive. my boyfriends birthday is the same day and his present is 60 dollars. so i kinda have a 40 dollar budget for her. i have NO idea what to get because she has everything already. She just got a 2010 kia forte koup so maybe i could get something for her car? but what? PLEASE HELP ME! any ideas would be very helpful! THANK YOU!