Be fully booked. Tell her your hours are now limited due to (insert reason, kids, husband, dogs, parents, study etc etc.) and you are currently full. You can text her if you get any cancellations (obvs you won’t)
Alternatively, take the opportunity to tell her in a professional manner that due to the issues she has had regarding her hair extensions, you feel you have done all you can and it’s now time for her to find another technician. Wish her well and say goodbye.