Calendargirl. I think you are very sensitive to the embarrassment and difficulty of escaping the "next appointment situation."
I wonder if the OP could go one more time and be prepared for the moment the appointment book comes out?
Maybe, as soon as she has paid, she could say, "I really have to go straight away, I need to be home by ..." and rush out saying no more. Or when asked "What about your next appt?" just say as she rushes out "I'll do it later". Which isn't a lie, but she'll do it with someone else!
If the chest HairDresser makes the Appt before taking the money, then OP needs to have the correct money ready and just hand it over and rush off....
If the appointments are set up in a block, such as every two months, first Tuesday... Then she can phone and cancel! Just cancel, too, don't get into a conversation. When phoning she can say "I need to cancel - sorry, got to rush... Goodbye" When HD tries to get her to make a different arrangement, she "must go, sorry!" or the door-bell rings...