Dd has one to one therapy once a week via zoom. It costs £65 for 50 mins, paid in advance for the month. Because it's half term we are out of routine and completely forgot. Therapist has my email and number and did not attempt to contact us. She sent an email nine hours before the session with the zoom link.
I am self-employed and run online sessions (not therapy, and much cheaper!) and if someone doesn't turn up, particularly for a one to one session, I would always send an email or text after five / ten minutes to check if they are coming.
While I accept it was our responsibility to remember, I don't think I'm being unreasonable to expect her to make some attempt to contact us when we didn't turn up considering how much we've paid (and she won't refund).