I'm so, so sorry. I just went through something similar with my best girl (Agnes, my sweet beautiful golden retriever), and hard as it was, I had to let her go. It's been about 5 weeks but I'm still heartbroken over the loss of her. Please PM me if you want to talk about it.

You did the most selfless, loving, courageous thing for your wonderful baby. It was the right thing, so please don't question yourself. My husband and I were w/Agnes when the vet put her to sleep and it was very, very peaceful. While I would give anything to have her back, I would not want to have her suffer as she did during those last few days.

My husband got me a votive candle after Agnes died. On it is a verse:
"Grieve not, nor speak of me with tears, but laugh and talk of me as if I were beside you ... I loved you so - 'twas Heaven here with you."

Your Kallie is waiting for you at rainbow bridge. My Agnes went and welcomed her, and she will make sure Kallie is taken care of until you can be with her again.