Originally Posted by yyzvoyageur

I'm your man for this question.

Don't waste your time going to Seattle. The airline will board her with her UK passport. Airline staff will simply assume she is a visitor to Canada. Don't confuse the issue by telling them otherwise. Once you arrive in Canada, she should explain to the CBSA officer at passport control that she is a PR but has not received her card yet. Bring any documentation you may have regarding her PR status. She may be referred to the immigration secondary inspection area in order to confirm her PR status. Prepare to be delayed slightly upon arriving in Canada, but if she is a permanent resident, CBSA will not deny her entry to Canada.

Enjoy your trip!