NO GIFT CARD! the four yr old will not appreciate it and the parents will hate you when they end up at Toys R Us spending twice as much as the card is worth! LOL
Kids at this age still love opening the present just as much as the present itself.
Wander into any SuperStore and head towards the toy section. There will probably be plenty of moms there to advise you. If not, anything involving a pony, dog, kitty, or, princess will do. Look at the age range on the package that will help too.
Make sure it's wrapped nice and she will love it.