Izzy is too quiet to say anything ,if Isla said anything the parents wouldn't do anything,the spiteful child gets away with everything for some unknown reason and she knows she can get away with itExactly I get that siblings have banter and itās fun, which is fine, but when itās no longer fun and the other child is clearly scared and struggling like Isla clearly was, then a kind person would stop, however much āfunā they were having. But she carried on as, like you said, sheās spiteful