She will need a study permit, she will not require a visa to visit (TRV).
The CIC Web site states "You must submit your application to the visa office that is responsible for the country or region where you live".
http://www.cic.gc.ca/english/study/study.aspThe current processing time for study visa's is 5 months (UK).
While I believe that is is possible for her to travel to Canada as a visitor and apply to the UK for a study permit, I would suggest that she applies before travelling.
In fact the CIC website says the same

Have you checked the CIC site regarding study permit requirements?