Take a look at the passage again:
Horrified, Sherri stared at her reflection in the
mirror. Hair sticking out in seventeen different directions, a spot
of whipped cream on her chin, and a green pen mark across her nose. Why
hadn't her friends at the table mentioned her disarray?
You chose the first part, Horrified, Sherri stared at her reflection in the mirror. This part has a main clause: Sherri is the subject; stared is the verb. A fragment will not have a main clause.
Go back to the passage to try again.