I would also...suggest you actually visit the dog pound. It's amazing that they don't always know their breeds. I knew someone who called repeatedly to the pound...and was told their dog wasn't there. And they went down and sure enough...HE SAT RIGHT IN ONE OF THE PENS! So...it doesn't hurt to try...Also...you could call the people who does care for the highway. The highway department maybe. And see if they may have sadly...cleaned up any dogs lately...I pray that isn't the case.
I hope you locate her soon. Hopefully someone picked her up and took her home...and just hasn't seen the posters you put out. I would also if you are on Facebook. Post an add with a picture...ask friends to copy and paste and share to get it out further...many of dogs have been relocated through Facebook.
Good luck to you...I hope she is found soon.