That reply is a terrible thing to do to a little kid. Just like perpetuating the Santa Clause/Easter Rabbit myths can cause distrust, this letter preys on a little girl's naivete to further someone's belief that God is real.
Better the kid gets the real story--Abbey's dead, it's all part of the cycle of life.
I was on my way to being an athiest at age 8 when I realized that my preacher and my bible didn't say anything about reunited with my beloved Bandit in heaven. And if God didn't want my dog, he couldn't have me. I already thought he was mean when he asked people to sacrafice lambs and drowned the whole earth except those on the ark....
I'm going to donate all my money to an animal shelter and punch Hitler in the face.
Better the kid gets the real story--Abbey's dead, it's all part of the cycle of life.