I'd say the solution is to become a food reviewer/influencer, and get people to let her in by clout...but I'm pretty sure that would count as unduly influencing humans, and thus be against Elma's code of honor as a Harmony Dragon.
There's another option that entails no conflict of interest. She could effect the reviews in a way that would allow her subsequently to identify herself to the restaurateurs (by, for example, logging into her reviewer account) but stipulate that she will not revisit the review. Some of the restaurateurs would, in gratitude, ensure that she can get a table without a great wait.
Honestly, Elma becoming a food critic is just about the best, most natural use of her abilities and interests . She should really concider making it a career
Clearly she needs to find so many good places to eat that the readers of her reviews do not cluster in any one restaurant, but instead are spread out. It also isn't like her deleting those reviews is going to do anything, you can bet that the places have them printed out and framed given how much business they got from it.