TheLadyLion and myself are still on track for our wedding at the end of March but the first anniversary of our first date is coming up soon. I’m just trying to decide if the anniversary of when we met or when we had out first semi-official date is more important. We met at a halloween murder mystery costume party last year but it was more out characters (a murderer for hire and a scheming society bitch) interacting than us getting to know one another. We had our first date a week later. This year I’ll of course do something special for both days but I think we’ll eventually choose one as being the more important.
My personal opinion: the date. It’s kind of what “started” the whole thing. The first time you met, there wasn’t necessarily anything begun yet.
I hope that makes sense.
I vote for the date–ours is the first hand-holding–but then I couldn’t tell you the date that we first met each other (and he doesn’t remember it anyway).
I think the date is more important, but it couldn’t hurt to do a little something (love note, e-card, single flower, etc.) for the day you met. It’s an easy way to “win points.” 
I wasn’t sure either, so in late August I asked my now fiance (getting married in May, yay!) and he said HE was counting from the night we met, not our first actual date, which was about a week and a half later. Since he had this idea that he HAD to wait a year before asking me (and he really wanted to be the one doing the asking) it was a big question for me. (Then he shocked the heck out of me by proposing over Labor Day. Men!)
Maybe you should just ask her?