Buy her something that she wants but wouldn't necessarily buy for herself. For example any shoes or purses that she's said that she likes but she hasn't bought for herself? Does she collect anything? You probably won't go wrong with jewelry.
Something that u put effort into to show her how much she means , a planned carefully evening out with a gift and flowers or a show that gets her out to laugh, or a day at the spa for pampering before dinner with you romantic, and has your attention on her