Might have been another child who said it cause I just cannot imagine anyone applying this to Willow? It is not a word we use either (Dominic is overweight mind you and we don't even tell him that!) but it is of course a word my boys picked up anyway but don't use cause I told them it can be hurtful when applied to people. Maybe they got it in a tv show? I think, but I might be wrong, that it is said to Daddy Pig in Peppa Pig, could she have it from there?