A brief follow up -- but first, yes, a Canadian Passport holder can transit through YVR the same way.

After getting the explanation from the CP agent, I decided to double check with immigration officials on Monday. What a mistake. They gave me non-sensical, contradictory answers, indicating the need for a visitor's visa.

After all that, I sent a long e-mail to Vancouver Airports customer serivce people. They responded the next day, with a length explanation of the exact procedure for a transit. They also included all sorts of other useful information, such as what happens if the connection is missed, what facilities are open at that hour, and so on.
(No she doesn't need a visa, of any type. If the connection is missed, then the airline will take care of all documentation issues.)

A very impressive, and quick, response from a great airport. They have a great web site as well -- check it out at :

http://www.vancouverairport.com/

Regards,

Ken Hamer