Sorry to hear about you friend. It's hard to see innocent animals suffer. At least you still got her. Just spend the time with her as much as possible and try not to dwell too much on the negatives. The thing about dogs is that usually doesn't matter how bad they feel, they always seem to enjoy your company and you can see it in their faces.
I still think of my dog who died a little over 2 years ago. I miss him.