I agree with pomeranian and would like to add chihuahua. IMO she's way too small for a border collie. A good way to find another dog like her is on petfinder.com.
A pom-chi is a designer breed and as you can see in this page, no two look alike, but the second to last photo on the page with a dog being held looks almost like yours but brown. http://www.dogbreedinfo.com/pomchi.htm