Hi there,
There are collars out there that have a GPS device attached to the collar that you can get. Here is an attachement as to how they look
http://www.environmental-studies.de/...lar/dog-1.html
They are a little bulky so I am not sure how comfortable they would be for a small dog.
Good luck and I am happy to hear that you got Mia back, I can only imagine how scarred you must have been. Maybe you even want to consider enrolling her to a dog class where she will get used to respond to people so that she won't run away.
Anita