she should first stop phoning and start writing
she should state that she is not responsible for someone else's unpaid CT
and state she is gonna pay what is payable after completion
she should be ready to prove ( = bit of paper ) the date of cpmpletion
if the ryedale site says the first four weeks is free ! then she should claim that
however it is worth finding out that if the house is uninhabitable ..... which hers is - whether it is exempt ( as of law not bye law )
https://www.gov.uk/council-tax/second-homes-and-empty-properties