Layover in Beijing, en route to Canada

My spouse is from Laos, I am from Canada. We are flying BKK-PEK-YHZ and will be doing a 8 hr layover in Beijing during the day and we want to travel to the Great Wall. I believe I can get a 72 hr free transit, when I arrive at PEK, as a Canadian citizen? What will she need to be able to go to the Great Wall with me? And what cost? If she can't get a visa to leave the airport will she be allowed to land at PEK and just remain at the airport until our connecting flight at least?
thanks for the help.. AJ