How to make someone forget something?

My sister was eating goldfish, and I reached for one, but stopped because i wanted to eat a little healthier. In response my sis picked one up and "open wide", so i told her no because i had an apple to eat healthier. Then she took the goldfish, said she was proud, then went up stairs. But ever since then she has been down my throat about eating healthy. Anytime I even have one potato chip she yells at me. How do I make her forget that the goldfish/apple thing so she will stop bugging me?