Numbers, I think it's best to wait until your sister is in therapy to avoid doing things to help her with her rituals, because behavior therapy is best done under a psych's advice. He may tell you to refuse to do the behaviors, but he might not start her out having the family completely avoid doing things for her. Gradual might work better for her. That said, I don't think you should do anything that is too stressful for you or that seems unreasonable.

You're absolutely right, Pup! While I feel for people who have to (or choose to) live with us and be involved with us, we have it far worse, because we can't run away.