Sometimes letting go hurts too much and people (children or adults) need to cry out a route to Goodbye. It occurs to me that this reaction is a way of saying "I can't accept this loss right now because <Santy><the Easter Bunny><my dog who died> might think I don't love him if I do, and I love him so much." Does that make sense? What I'm saying is that maybe, in this case, she's mourning a loss.
Some people feel things very deeply, and loss or pain that occurred in others can sometimes feel worse than one's own pain. Not physically worse, but emotionally. It's especially bad when the one who's suffering was defenseless and hadn't done anything to deserve the bad treatment.
Things like this are always worse when after a long or tiring day, or when there's a triggering event. For example, say a child is upset about the loss of a family pet and then someone mentions that the dog down the street is sick. The sick dog can trigger sadness about the family pet. So there would be two issues feeding into each other, with a net result of a synergistic effect on the emotions.
As for coping strategies, it might help to talk about keeping Santy in your heart. If everyone walks around with a bit of Santy inside, he'll always be with us in a way.
For future things like the past problem with the boy in school, she could make a hand-drawn card to say she's sorry. Or she could just be encouraged to say, "Joey, I think I was mean to you and I feel really rotten about it and I'm really sorry."
If it makes you feel any better, any child who feels so deeply will probably grow up to be a wonderful adult.
HTH,
Val
