When is her appointment ?

You want to cancel or reschedule your appointment

You can cancel or reschedule your appointment using your online UK Visa and Immigration services account.

You must:

Cancel at least 5 working days before your appointment
reschedule at least 48 hours before your appointment

You’ll be refunded the full fee for cancellations made at least 5 working days before your appointment.

You don’t need to pay the fees again if you reschedule your appointment.
https://www.gov.uk/ukvi-premium-serv...an-appointment