Since the question does not have multiple choice answers, i would answer the question as much as i can.
Answer:
Sally has breached a contract
Step-by-step explanation:
Sally will lose the dispute between herself and the stylist because she breached the agreement she has with the stylist that she will pa extra $40 for getting highlights.
This is because as soon as Sally agreed to pa extra $40, an agreement was reached and hence the refusal of Sally to pay for the highlighting service means that the stylist has been short-changed as she is earning less for more service that she has rendered.
Cheers.