I think I would have packed up the quilt, taken it home and put it away until a day that the two of us had time just to be together and had a chat with her. Or would have waited to see if anything was ever said about 'the missing quilt'. Maybe the possibility of them giving it back to her when she 'grew up' would have made more of an impression on her. Kids today have a sense of 'entitlement', but not appreciation.
Chris