I would say to her "they say if you don't have anything nice to say, don't say anything at all." Then tell her that if she can't find something else to talk about, it's best not to talk to you at all because you are trying to keep positive and think positive about others. And then tell her, "they also say that scowling when they are talking bad about people causes those little lines to appear between her eyebrows" like she has. (I don't know if she has but she will be looking at herself in the mirror where she needs to be looking anyway.) Sorry, I just do not like people like that.