So sorry. I have to deal with these things almost daily (I'm an ER vet) and it always breaks my heart, even after all this time. I know it sucks, but please know that you made the right decision.
It has been a rough morning...to top it off, I ended up locking the keys in the truck through all the excitement, so now I am waiting for AAA so I can get to work (not that I feel like going today...).
Shelby, I'm so sorry for the loss of your friend Kenzie. It's always so hard to make that decision, but as a responsible pet owner, you knew it was right to put poor Kenzie down instead of having her go through surgery. My prayers are with you, your family (and Casey) as you go through this tough time.
I am so sorry for your loss. What an awesome person you are for rescuing her. It sounds like she had a wonderful life with you. It hurts so bad when you lose a pet because they are like our children. Lot's of