Poor Lucy! And poor you! I think that you should take Lucy to see a vet, since maybe she has some kind of infection or problem that she is trying to not-so-subtly tell you about. Maybe she's refusing to use the litterbox because it hurts for her to go, which seems likely if her anus is red and painful. If she's 2 years old and not using her litterbox, she's definitely telling you something! At least call a vet's office, perhaps, because often they can help you diagnose the seriousness of problem. Hope this helps and good luck to you . . .