Old Customer Claimed I Overcharged; I Refused, She Panicked

I'd run my restaurant for five years. One of my regulars booked a private dining room with me every holiday. She had someone to impress, so she booked a full seafood banquet ahead of time, and I charged her only my bottom price, 999. She looked at the bill, turned around and went to another place, then started making snide little comments in the group chat. "Some restaurants, once business gets good, they start gouging their loyal customers." "Same dishes, and the other place quoted me half the price. Now that's a shop that knows how to do business and has a conscience."