<human>: Could you distill the essence of the text into 1-3 sentences?

I've been single for about two and a half years now.  I was in a long-term relationship that blew up quickly and once I got over it I decided to look out for myself for a few years instead of trying to get a rebound date.

There's a girl that I went to college with who's two years younger.  Since the moment I met her (5 years ago) I have absolutely adored her.  At the time I was very happy in the previously mentioned relationship and put zero consideration into blowing it up.  In the time since then we both went through break-ups, so we've never been single at the same time.

The other day I'm browsing the online dating site I'm on and she pops up as "compatible".  I had suspicions that she broke up with her boyfriend and this confirmed it.   I don't know her THAT well , but we've always gotten along; when I run into her I always see a huge smile and get a big hug from her (and sometimes she calls to me from a distance if I don't see her).  I've only seen her a few times since I graduated, so we've haven't really stayed in contact.

Now, I have two main concerns with pursuing her:
1: I don't want to come off as going for her simply when she's on the rebound.
2: I ALSO don't want to come off as a big brother type trying to make her feel better.  

I don't have her number, so do I send her a message on said dating site?  Or send her a message on Facebook?  If it helps at all I will most likely see her at an alumni event in October, so should I wait until then?
<bot>: I want to go after a younger girl I know that just had a break-up, but I don't want to come off as a rebounder or as someone just trying to make her feel better.