Only time will make it better!
It will always hurt, always be sad but the pain gets less as time goes on.
My first dog has been gone just over a year and I still feel so guilty over the way she was PTS. I also still get teary thinking about her, I don't often read this particular forum because it brings all those sad feelings up again.
BUT - I can now also think and talk about my Maxi and laugh about some of the silly things she used to do.
You will never forget your little girl, once it stops hurting quite so much let yourself think about some of the happier times you guys had - don't dwell on the bad things, you did everything you could for her!