While what you did was very human, there might be a kid or guy out there who is very heartsick about loosing this dog.
It is great you want to keep her, but I know down in my heart that after loosing my dog once how upsetting it is as it is often just like a death in the family.
Somebody might be still looking for this dog. I would spend some time and post pictures on the websites that handle these...I would also notify the humane society in the areas surrounding your find.
If nobody comes forward...then you can go to sleep knowing you tried really hard to save the day for someone....sweet as that dog is, I know I would be burnin the oil trying to find her...but those dogs can travel a long way from home, particularly if someone sees her and and drives off with her only to lose her again well away from home. She would escape and keep looking for her owner...which she might do with you.
In the final analysis it is up to YOU to find the owner, as the dog can't do it. If you never turn him/her up, then you gave it your best shot and welcome to one fine companion.
http://www.lostyourpet.net/default.aspx?countryid=2
http://www.lostdog.com/
http://www.lostdogsearch.com/
http://www.pmia.com/