Not that I'm agreeing with Lizzy, but when judging her character, I like to think of what she knows about Anne. Anne very rarely troubles herself to go in when she visits the Collinses and makes them instead come out to see her, whether or not it is comfortable or convient for them. She thinks only of what is comfortable for herself. From this Lizzy sees her as unfeeling and selfish (if she is too ill to come in , why is she visiting at all), and therefore feels no pity for her.