for your own piece of mind you should try everything in your power to see if someone is missing her. I'm sure you are hoping she is in need of a good home, and if she is- then I am sure she has just found one. But just think how you would feel if she were your baby that was missing...
BTW- I know all my yorkies can run around in the grass, mud, weeds whatever they can find and look "homeless" in about 5 minutes time
- so unless she is under-nurished, she may not be as "abandoned" as she looks.
Let us know how this story turns out!
Best wishes!