I am so sorry your dog died, Charley.
It is very sad when the ones we love die. I know you loved her very much, and it may be hard for you and your family for a little while. If Kasey was very sick and suffering, I think this was for the best. It would have been cruel to prolong her existence if her illness was terminal and the extra time just meant more suffering.
My advice is when you think of her, try to focus on the happy times. Remember, a bit of Kasey will always be with you, in your heart; and with us, through the pictures you posted.