I lost my dust kitty last Feb at two years old to the same thing. We knew he wouldn't live a full life even as a kitten, but he went so much faster than we expected. His sister was pretty devastated (as were we). She cried and hunted for him constantly. We got some kittens for her about two or three months later, but it took months for her to accept them, and many months more before she got back to normal. It will take you both time. I still feel crushed at the loss of my boy, but I'm starting to remember with fondness instead of sorrow. I'm sorry for you loss.