Ben,

You really should have posted your question in a new message thread. The short answer to your question is yes, the polygraph can be beaten. See Chapters 3 & 4 of The Lie Behind the Lie Detector to learn how. More importantly, however, your idea of having your girlfriend submit to a lie detector test is misguided. Polygraph "testing" has no scientific basis whatsoever, and actually has an inherent bias against the truthful. Whatever questions you may have about your girlfriend's honesty, the answers are not to be found in a polygraph chart reading. You might as well consult Miss Cleo.

For examples of the harm that misplaced faith in the polygraph has caused for others' relationships, see the message thread Domestic relations polygraph.