She's an elderly lady showing her appreciation for your help. Buying your grandchild a little present is quite appropriate and not in any way weird and wonderful. I could understand your distress if she was, perhaps, offering you large wads of cash. The poor soul doesn't realise that her good intentions are driving all of you, inexplicably, to the edge of a nervous breakdown. I suggest you graciously accept the gifts and donate them to charity. I can assure you that there are plenty of children who would be thrilled to receive them. Then find something more important to worry about.