17 yrs old from Canada

There will be no problems if she is traveling on the itinerary:

Montréal - Beijing - Singapore

And if she does not insist to leave the airport.

So, she will just declare at check-in in Montréal that she will travel to Singapore via Beijing using 24 hour visa free transit. Shortly after, she will be allowed to board the plane.

Upon landing in Beijing, under the conditions that she flies on a single (through) ticket by Air China, she will just clear a couple of formalities like security check, ticket check and similar and she will proceed to her boarding gate for a flight to Singapore. She is advised not to try to exit the airport because there is no need to complicate her transit.

THANK YOU SO MUCH...A RELEIVED PARENT. BUT DOES SHE NEED TO APPLY FOR A 24 HOUR FREE VISA? REGARDS ERIC

Actually, there is no 24 hour free visa, but it is 24 hour visa free transit. In other words, 24 hour visa free transit is nothing you are applying for or something that you will receive. It is a right to travel through China on an itinerary that has less than 24 hours of transit time within China, counting from the first scheduled landing in China, until the final scheduled departure from China. Your daughter will have 7:50 hours, so she is allowed to enjoy this right to transit or better to say she is eligible for 24 hour visa free transit. She will not apply for anything.

As I have mentioned in my previous post, she will just accomplish several formalities (security and similar) upon landing in Beijing and if she is traveling on a single Air China ticket, she will just wait for her onward flight within the transit area of Beijing airport. She will not have to apply for a temporary entry permit and this permit is the tool that allows a traveler to exit the airport. She will stay away from this because there is no need to complicate her travel. I understand that she might be a bit curious to exit the airport, but it is not advised at her age and by the fact that she is traveling alone.