odroku, chances are if I'd been in the same situation as you I'd feel just as guilty, and would be beating myself up just as much.
But, take yourself out of it, and look at it from an objective viewpoint. Re-read your first post as if someone else had written it, and how they called to the dog, tried to grab her in time but couldn't, but did take control of the situation by securing the dog in the house immediately.
Then, after going back out right away to give the other dog's owner their contact info, (you know, doing the responsible thing, we so seldom see these days), and finding she had left, they drive around the neighborhood looking for the lady and her dog.
So, they don't find them, the come to an internet Community Forum to post about the situation, as a means of hopefully getting in contact with the woman, or someone that knows her.
To me, you've done evrything you can so far. To be honest, I've become quite cynical over the years. My personal thing, being a full time pedestrian/bus rider, is that 99.99999935786% of drivers out there don't give a rat's patootie about pedestrians what with how many of them blast into crosswalks to make their right turn on red, or blast out of store parking lots. So, if I have to stop dead in my tracks, to prevent becoming dead by someone elses carelessness when I'm legally crossing a street, I'm gonna glare at them. And even if they do the OMG! I'm so sorry! I didn't see you! gestures, I'm going to continue to glare at them because I assume they drive that way all the time. Conversely, if I had been the one in that lady's position, I may have thought evil things about you, because I wouldn't be looking at the situation objectively, I would just assume you let your dog run wild all the time, but that would just be my cynicism coming into play.
But by posting here, you have shown you have a conscience. Many people would not have driven around trying to find the lady. Many would have not posted publicly to try to locate her, and risk being berated by others for perceived carelessness.
So, as SDA said, use this as a learning situation, and make sure your dog is securely leashed before you exit your house, and perhaps look into some type of training. I hope all of this made sense.
There's still a few hours of sunshine left, so relax and enjoy it, and give your girl a hug!
Mike