I am so very sorry about your dog. I just had to put my dog of 11 1/2 years to sleep on Christmas day. I still cry every day. Today has been an especially bad day. It's a beautiful day here, one that I would normally take Beau for a walk in the woods. He loved walking, and like your dog, got me through some pretty bad times.
I hope that time lessens your pain. As for the teacher, as a former teacher I suggest you request a conference with the teacher and the principal to explain that your dog was like a sibling to your daughter and she needed time to grieve. Good luck.