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I just went through YVR on a SIN-NRT-YVR-SEA itinerary Friday.
YVR is preclearance so luggage will be checked through, she will get it in SEA.
Yes there is passport control but it’s to the U.S., you end up in the transborder part of the terminal as formally having entered the U.S.
They’ll take NEXUS and Global Entry.
Her connection is tight but I wouldn’t say you have no hope of her making the connection.
If she doesn’t it’s up to Air Canada to rebook.