Well I DO get your post (not that hard people!). I can certainly understand why you'd be upset, I would be, too. You tried to remedy a situation and it went nothing like you'd hoped. And probably at the root of it all you picture this sweet little dog. However, the boys didn't really do anything wrong either. I'm guessing his parents weren't prepared to host a dog, or didn't understand what their son was asking, and they did what they thought was right- taking it to the shelter.
It's easy to look back and think clearly about what should have been done. If you had the time, you could have arranged things different for your own schedule to be more able to help out. But things like this don't happen with time to plan, we have to make quick decisions and that almost always leads to doubts and regret. You all had good intentions, life just got in the way.
And you are going the extra mile to post on Craigslist and try to find a home for the sweet little thing. Even considering adopting her yourself? Wow, you have a sweet soul and have NOTHING to feel bad about. You are doing the best you can for the dog, nothing to feel bad about. I sincerely hope that you find a home for her, or that the shelter does. Be proud that you are looking out for the dog and did what you could, no matter what happens.