Airlines tend to be very carefully when the cardholder is not one of the pax.
Unless the card is verified before the flight, you can be in real trouble.

I don't remember if CX does it on its website booking system, but some airlines do ask if the cardholder is travelling on the booking If not a verification process has to take place. If you book through a TA, that is usually a different process.


AT the very least, your sister should take the expired card with her. Hopefully the surname matches.
As to the likelihood of a challenge, it depends on so many parameters.....
If the card has been verified at the time of booking, for example a Visa card with Verified by Visa, that should not be a problem. The only time, I was ever verified at check-in was when I paid to the airline by phone. And that was my own credit card.