buy her porn.
girls love porn and really appreciate the statement you're making with such a gift. it shows you care.
make sure you get some good girl-on-girl porn, because that lays the groundwork for real life girl-on-girl action. perhaps you've already thought about some of her friends that would fit the bill. invite them to watch, too, "for a laugh". again, your girlfriend will really appreciate the message you're sending with this gift
and don't forget the rufees! rufees are like a box of chocolates to that bouqet of porn you brought.
and, remember. it's about her, that's why you've made this gift so special.