I feel both for you, LRavenscroft and for the poor woman forced to answer a phone when her English is not up to it!
You are the customer and have an arrangement, so you are fully justified in expecting your hairdresser to know that you come as usual with newly washed hair. I would not bother going in the day before to confirm this, but I might phone and ask to speak to my usual hairdresser.
As to the receptionist: I changed language and country at the age of 16 and spent two horribly embarrassing years gradually improving my language skills in my new language, and dreading having to use a phone.
Face to face conversations are far easier, as the person you are talking to can see when you are at a loss and usually help you out.
The phone is the devil's invention at this linguistic stage as the person on the line cannot see whether the receptionist is genuinely at a loss or just being difficult.
Someone has to answer the phone, and her language skills will only improve through use, but honestly whoever runs the business should try and help the receptionist, or simply take her off the reception desk until her English is up to answering the phone.