Hi @Jeanette32,
It is understandable that you do not feel comfortable with a guest coming that isn't the one that booked.
Unless using a special business account, third-party bookings are not allowed - according to the Airbnb terms, you may not "unless Airbnb explicitly permits otherwise, request or book a stay at any Accommodation if you will not actually be staying at the Accommodation yourself".
There is another thread on this topic here.
You should therefore contact Airbnb and explain the situation to see if they can cancel for you penalty free. This Community Help Guide explains the best ways to get in touch with them.
I hope you can get this resolved!
Kirstie