@Jane563
Let me get this straight.....she is travelling, has lost her mobile phone but, is still able (miraculously) to communicate that she is lost and needs to cancel!
The problem you are faced with here Jane is, she will be offered the opportunity to leave a review because the cancellation was on the designated arrival day....she has you over a barrel!
It is probably that Airbnb will side with her as the guest because, guests make Airbnb money, hosts cost them money......and as a host you are expendable at no cost to Airbnb!
Jane, keep all your communication with this hustler through the message stream so that you have a record to refer CX to.
Good luck, I hope you can sort this out to your advantage and if there is any further advice we can give please let us know!
Cheers......Rob