Plans move, and the thread can carry one move. Push the hour or the date once, at the desk's discretion, before she sets off and provided her diary has room; deposit and terms travel with the booking, and without an agreed new time the original stands. Change the restaurant, extend mid-evening: each is a single message, re-quoted when the format changes and agreed before it stands, at the same rate. Ending early is yours to decide and leaves the figure as it was.
Cancelling is a message in the same thread, and it is charged. Short bookings, three lines: beyond 48 hours before the start, the deposit turns into a credit good for 12 months; from 48 hours down to 24, half the figure; inside 24 hours, or a no-show, the figure in full. The long formats run the same three lines on a longer clock: beyond 7 days, credit; 7 days down to 72 hours, half; inside 72 hours or a no-show, the figure in full. The deposit is never paid back; it covers the charge first, and the rest is invoiced. The terms print the full line.