Calling off, and what the notice decides
Cancelling costs whatever share of the fee had already been earned when your message landed, and the notice in that message is the only thing that decides it.
There is a three step scale and nothing behind it. It is read from the moment your message arrives in the thread, not from the moment you decided.
The three steps
More than twenty-four hours before the booked time, nothing is kept and everything you sent comes back. Inside the final twenty-four hours, with her still at her own address, half of what you sent stays and half is returned. After she has set out, what you sent stays in full. Two things soften that last step: if the hour is taken by somebody else it all comes back, and if you can show the house lost less than it held, only the smaller figure stays.
What it is never
It is never damages and it is never a fine. The house does not claim a sum beyond the fee that had already been earned, and a booking with nothing sent ahead leaves nothing owed at all if you call it off before she leaves. Once she is on her way, that booking costs the share of the fee her journey represents, and that is the end of it.
Weather is not force majeure
A forecast that turns, a day of rain you had not planned for, or a cold that arrived overnight are all ordinary changes of plan and read on the scale above. Force majeure means something neither side can steer: transport shut down across the city, a serious disruption, an official instruction that makes the journey impossible. In that case nothing is forfeited and what you sent becomes credit against a date you can choose later. The full terms carry the worked examples.