Dear Sarah,
Show her this website and tell her that you are very sorry for being short in those best moments on the table with her during dinners and lunchs but it’s not something you can cope with and she has to understand you. On the other hand she has to respect you too and be more careful while eating, for ex. avoid eating noise making foods like nuts, apple or carrot if she doesn’t have to. I accept that we are allergic to some sounds but the counter part is also as guilty as we are.