Yeppie, if you do not know what to get for her, the best present you can give is more attention.
I have to admit the only time when I do not know what to get for my gf is when I have not paid enough attention to her. Come on, on your dates, she's bound to tell you something that she likes, a watch, brooch, ring, furniture, book, dinner at a particular restaurant, etc. Pay a little more attention and you would not be caught in such a fix.
Here's a few things I did or got for her the last few times I had difficulties for gift ideas. Maybe it will help.
1. Diamond ring
2. Dinner on the cable car (Call 100 to find the number. I forgot.)
3. A cheapo wire holder (Not recommended)
4. Flowers (SOP)
5. Soft toys (This gift can get tiresome is given too often)
The bottom line is you are the best person to know, not us. We have not been courting your gf. Give every moment of celebration she has a time to remember. Remember pay attentionto her, you don't want to regret losing her, unless you do not cherish her in the first place.