We always assume that any recipient of a PCN has used common sense and tried Plan A, which is to always get whoever contracts the parking operator to get it cancelled.
Plans B, C and D are what we deal with here.
What you need to understand for future reference is that the recipient of the NtK, the Keeper, should never, ever, EVER identify the driver. Only the driver is ever liable. Unless the operator is able to rely on PoFA 2012 to be able to transfer liability from the unknown driver to the known Keeper, then blabbing the drivers identity, inadvertently or otherwise, is the proverbial shooting oneself in both feet with a single bullet.
In this case, the location is the Radisson Hotel at Manchester Airport which lies within the Manchester Airport boundary and is therefore land that is subject to statutory control (airport byelaws), which means that it is not relevant land for the purposes of PoFA and so, had this continued to appeal and beyond, as long as the driver is not identified, they would eventually have nowhere to go with this PCN.
Luckily for you, your daughter has written confirmation that the hotel has told their agent to cancel the PCN. Don't be surprised though if ParkingEye turn around and say they will not cancel it and they want £20 to cover their costs.
As long as there has been no admittance by the Keeper that they were the driver (whether they were or were not), there is no basis in law for ParkingEye to pursue the Keeper for any money.