Ratings and Reviews:
Anybody who wants to eat out, checks the restaurant review online first, which include ratings about the food and comparison with other restaurants. The restaurant with good ratings is likely to fetch more customers, which is why it is advised that restaurants can hire reviewers or invite reviewers to rate their restaurant and its food.
If the reviewer does not like anything then ask them for feedbacks and promise him/her that it will be taken care of, so that she can mention these things in the review which work as reverse psychology.
Moreover, you can also send her a token of gift or invite one more time, so that she can analyze your dedication in your brand, which indirectly is noted in the review and will work in your favor.