@Amber553, may I suggest that they do an "Alteration" for a future date with the same Host?
It's one way of working around it and may work out to be a win-win.
If your sister messages the Host with future tentative dates and asks for flexibility, subject to when our borders reopen.
It's neither Guest, nor Hosts doing what's going on and very unfair, especially for older people who should be enjoying life free of stresses.
All the Best
Central To All Home and Location, Remuera, Auckland
As a New Zealander I'm sick to death of the stupidity that's going on as we all need to get our lives back on track for our economies.