That is a good question. Her favorite candy and a card is a nice start. What does she like to do? I once packed a picnic lunch and took a lady i was dating out for lunch that way for her birthday. I even packed a little cake with a candle and sang ( horribly) Happy Birthday to her. Think about her likes, sometime something that you make yourself that comes from the heart is the best gift in the world.
don't worry ..anything works fior the first time ..your gonna make LOT'S of trial and terror mistakes ..best plan ..flowers ..unless she has allergies ..or yah shoes..but a gift certificate,,fits all sizes ..if she has a car .. a gas card..or...hell I'm 60 an' still learning..good luck!!
How well do you know her? Has she ever made a comment like " I would love to do --- someday..."? I bought my wife a skydive jump for her birthday once. It was one of those things she had always wanted to do "someday...".