I would also be subtle and say something innocuous like..........."hey fatty bum bum
you sweet sugar dumpling, hey fatty bum bum, let me tell you something"......OR............"would you like to be a model when you grow up?..........then stop gorging yourself on cakes then!!!.".
Bless her.......at only 4, she is heading for a life of misery and bad health, if she does'nt lose some weight.....and soon :0 ( ( problem is Christmas next.......and we all over eat at christmas, dont we? )