If she qualifies for a work permit, it generally takes 20-30 minutes to get the work permit at the port of entry.
To qualify, she must EITHER be offered a job for a NAFTA-qualifying job (see FW 1 from the CIC website for a list of such jobs, or the NAFTA agreement itself, which has the same list) OR she must be offered a job for which an employer has received a positive Labour Market Opinion letter. She takes the job offer, LMO (if applicable), $150 (work permit fee), two photographs, the completed "outside Canada" work permit application, and evidence that she has the qualifications for the job to a POE offering immigration services and they issue it immediately. For some jobs a medical examination is also required (health care and working with children).
She can also send it in to a visa office in the US, that takes about two months. Or she may also be eligible to apply from inside Canada, which also about two months as well. That's why I suggested the POE approach.
US citizens have the easiest time finding and getting jobs in Canada of any foreign national.