If you have a charge per extra guest, then multiply this by the number of nights she will be staying. Then go to the Reservation and Send a Special Offer for the TOTAL cost of all accomodation for the group, plus your cleaning fee.
Do not add the AirBnB service charge - they will do this automatically.
Your guest will need to accept the Special Offer and make sure they do - otherwise you will just get the original amount.
We always email the guest letting them know that we have sent through the Special Offer and that they need to accept it to make it valid.