Sally Goes to Have Her Hair Trimmed and Agrees to Pay

Sally goes to have her hair trimmed and agrees to pay $40 to the stylist. While there, Sally decides that she would also like highlights. The stylist informs her that highlights will cost an additional $30. Sally agrees to the price, gets the highlights, but refuses to pay the extra amount. What is the likely result in a dispute between Sally and the stylist, and why?

A) The stylist will win because she did additional work in exchange for the extra payment and, therefore, Sally's promise was supported by valid consideration.
B) The stylist will win because she did additional work in exchange for the extra payment and, therefore, a valid unilateral contract existed.
C) The stylist will win unless Sally can show that she had previously received both a trim and highlights for $40. If she can prove that she previously received both for $40, then the past expectations rule applies.
D) Sally will win because the stylist had a preexisting duty to have her hair looking as good as possible.
E) Sally will win because there was no valid consideration in exchange for the highlighting.