I know I always focus on the wrong aspects of stories but I can't stop thinking about the issues the step sister must have. I'm 29 right now so 21 wasn't all that long ago for me. At that age I would NEVER have dreamed of doing something so spiteful and evil to anyone, let alone a child. If she can be so careless with treasured belongings, what can she also be so careless with? People? :( I would be seriously concerned about letting her spend any unsupervised time with the younger kids.
Good job for coming to rescue Grandma and making a new one. I know you must be very sad over the loss of the first one but hopefully time will heal that wound for both you and your grand daughter.