She probably doesn't want flowers because she wants something different this year, and you've been getting her flowers. The best gift you can give her is quality time and attention. If you can't do that on her birthday, just give her a card saying to set aside some time this weekend for awesomeness. Possibilities, depending on time/budget/personality:
1. Make her a fancy dinner, get a bottle of her favorite wine, some candles, and put on quiet music. It's better than any restaurant, in my opinion, and can be done pretty cheaply.
2. Take her out to a B&B in the countryside for an evening this weekend. Spend some time wondering the countryside together just enjoying each other's presence.
2a. Drive to a state park somewhere and go camping this weekend. If you two are outdoorsy sorts, sex in a tent can be a lot of fun.
3. Take her on some kind of adventure. Depending on her personality, that could be skydiving, rock climbing, hiking above treeline (if near mountains), driving a sports car, taking her to an awesome concert in town, the like.
Basically, you want to remind her how awesome her life is. That's what I look forward to in a birthday present.