Typically:
"What is the purpose of your trip to Canada?"
"How long do you intend to stay in Canada?"
If she's already been approved for the visa, she doesn't have much to worry about when arriving, as long as she gives the same reasons she gave in the visa application.
See ENF4 7.5 and 8.9 for more info.
http://www.cic.gc.ca/english/resources/manuals/enf/enf04-eng.pdf