Being a computer nerd/bachelor/hermit I'm not much help with the wimmunz. People in general expect that stuff. I never give gifts or cards for any occasion, I don't even own a tie, but I'm weird.
If I felt "slightly odd" about doing nothing, I would do something. But not just purchasing the usual thing that people expect. I would do the unexpected, because nobody expects it
What that is really depend on her, since I don't know her, you are on your own. You know what she likes, focus on that.
Sometimes people just go out to dinner. Hmm maybe you make dinner for her, she might get a laugh from that if you don't usually do that
Rent the movie Friday the 13th. 13th... get it