Well, for a start, she shouldn't be applying for SET(M) anyway, since she won't qualify for ILR for another 2 years. She should be making an appointment for FLR(M), not SET(M).
Secondly, I believe she will have to create a customer account in order to book an appointment online... so she'll need to create an account instead of using the 'Continue' button, and then log in first before she can book the appointment.