It's never easy saying farewell to the family pet. Never. I think it may even be more complex when it's your child's pet.
As their caretakers, the burden is ours to decide when a pet's right to a peaceful and painless end is more important than our grief and guilt over saying goodbye. Sometimes, we must do this on our children's behalf as well, which adds to the grief and guilt we must weigh.
If this beloved pup could have talked, I have no doubt she would have let her people know, "I ruff you, too."