Emma's failing to do her duty by Miss Bates, and subsequently Jane Fairfax, is a snub of sorts. She snubs Robert Martin by declining to be introduced when they meet on the road. She arranges for Harriet to snub the Martins by returning their previous kindness with a perfunctory visit. You could also say that she snubs Elton by making it clear how far beneath her she imagines him to be when he proposes. These are the only instances I can think of off the top of my head, and this far into the story. I can only imagine that her snobbish behavior increases for a while yet.