My interpretation is that the fish didn't actually turn down and punish, but fulfilled the wish. It's just that the fish thought: to be like God means to be humble. She asks to be like God, true godliness is humility. So she did get what she wanted, but not in the way she thought. (BTW I'm not religious in the sense I go to church a lot, and don't even necessarily believe in God, but I do share many of the values of religion.)