If you have lived together for 12 months or more, you can fill out a declaration of common law relationship. Take it to the border with your $150 and when you re-enter Canada, tell them that she wants to apply for an open work permit based on your work permit. You can also apply for her work permit without leaving and coming back but then you will have to wait for it. Here are the forms:
http://www.cic.gc.ca/english/information/applications/extend-worker.asp and you would have to send the declaration of common law also and a copy of your work permit. Applying online is faster and apparently you can upload the forms on there.
If you haven't lived together for 12 months, then she is not your common law and as she is not your wife either, she would not qualify for a permit until you had either lived together for 12 months or gotten married.