Because it's CX then it's going to be over to CX to come up with a replacement, presumably a later service to BKK. If this change has just happened, I would leave it a week before even looking at it, assuming it's some way off. She could just do nothing, if the HKG service looks viable then CX would rebook her if she missed the onward service. You can call up to force the issue if you spot CX redemption availability in any cabin to BKK, then it's an easy thing to do.

Zero chance of being rebooking on to other airlines if it's some way off.