Take a look at the sentence again:
With sharp scissors, Thinh tried to even her client's hair, but the woman
kept twisting in her seat to yell at her two small
children who were terrorizing the salon,
Thinh finally decided that crooked ends were better than poking out a client's
eye.
The woman kept twisting in her seat to yell at her two small children is a main clause. Who were terrorizing the salon is a subordinate clause. A subordinate clause is an incomplete thought and must be connected to a main clause. When a subordinate clause follows a main clause, you often do not use any punctuation.
Go back to the sentence to try again.