G.B.
I can't imagine the humiliation she feels when her friends see she is still in a car seat when most of them are probably not in anything but a booster and seat belt.
I think you have to weigh this carefully. When she rides with anyone else she'll be in just the seatbelt after her birthday. If she needs a ride somewhere and you volunteer to take other kids they'll make fun of her in a car seat so you are sort of in a bad place.