Answer:
3) She can watch her employees work to determine the cause of the problem and then respond appropriately.
Explanation:
The proper thing for Jill to do is observe how her employees actually work, or if possible get someone else to observe how clients are being served in her restaurant. Maybe her employees will try harder if they see her around, so the information that she collects will not be valid for the time when she is not around. That is why using someone unknown to their workers might result in more realistic information.
Then after she has all the necessary information, then she should act accordingly. Maybe those clients just like to complain a lot or maybe they were right and some things must be corrected.