How can I block a specific persons status updates and always appear online to that person?

I have an ex who I still speak too, but I am struggling getting over. I don't want to delete her from Facebook. because she has done me no wrong, and I think in the future we could be friends, but right now Its very difficult. So all I want to do is make it so I don't see her status updates and that I always appear offline to her. How do I go about doing that?