The imminent death of your long-time companion is understandably causing you to feel many intense emotions. I would strongly suggest that you do not take your five year-old daughter with you to the vet's when she is put to sleep. This is not something she can handle emotionally or intellectually at her age and stage of development. I would also not use the term "put to sleep" when it comes to telling her what happened to your dog at the vet's. She could begin to associate being "put to sleep" with dying and this could give her unnecessary fears about her own bedtime and you and other loved ones going to sleep. She should be told that the dog was very old and became so sick that she died -- her body just couldn't work anymore. You could also mention that the vet and you helped her die without her being in pain.

There are many superb children's books that help kids your daughter's age move through the loss of a family pet. Ask your children's librarian and your vet for their recommendations. Books by Alan Wolfelt and Earl Grollman are good resources for these discussions. Encourage your daughter to express her sadness and confusion, while not being afraid to express your own sadness and sense of loss.