How does one deal with other family members who simply detach and refuse to help?

My sister is case in point. She completely distances herself from us and we too have broken off all communication from her. It's difficult to carry on a conversation with a person who gives you one word answers. I'm truly starting to resent her and her intrustions in our lives. She comes over on Sundays, when she feels like it and we never know when/if she will "appear". It is ludicious. Last week she came here unannouced during the dinner hour, refused our offer to eat with us and then proceeded to sit with dad while he ate, IGNORING US COMPLETELY and making everyone feel incredibly awkward that she chose to stay. What does one do with this?