Dear Dog Daze,
Losing a pet when you're five-years-old and have had your whole life can be quite traumatic. The best that you can “say” is to mirror back to her what she says with compassion and empathy. You can also assure her that she will feel less sad and angry as time passes.
If her parents have not had a memorial ritual for the beloved pet you could speak to them about that. You and your niece and make a photo album of the dog, your niece can dictate a goodbye letter, you and your niece can put the dog’s dishes and toys in a box and bring it to the local pound, or you can cook a special meal together and enjoy it in her dog's honor.
There are many books about losing a pet you can check out the one(s) that are appropriate. Lastly, her nursery school teachers are experts in how to mourn the loss of a pet and you and/or your niece's parents can consult with them for advice.
I hope this is helpful,
Natalie Robinson Garfield
TheSenseConnection.wordpress.com
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