@nprofile1q... Have you found their nest yet?
Carpenter ants can be VERY difficult to track back to their nest. They seem to have a behavior pattern where if a large animal is tracking or tracing them they won't run home as many other ants will. They will lead you on a wild goose chase. (Can you guess how I know this?)
If you want a carpenter ant to lead you to her nest you can't let her become aware that you are watching her.