If it was me, I'd find out how to contact her, and simply sasy, "I'm a guy, I was completely oblivious, and I'm very sorry". Might help her move on, and it's a 'good guy' thing to do.
<waits for others to say, "this is a bad idea"...>
Nah, I don't think so. We have mutual friends on Facebook but I have not tried to friend her. This was over 10 years ago. I'm married with two kids and I'm pretty sure she is married with a child now as well. I think I'm just going to leave this one alone. Like I said, I don't even really know her. I went to high school with her and gave her and her friends a ride one night. That's pretty much it. I didn't tell this story as a way to ask advice, I just thought it was food for thought pertaining to the topic. I don't feel particularly guilty over the situation as I never mistreated her or badmouthed her. I was always cordial with her when she greeted me at school. Just something to think about. She is obviously over it by now.