It is not unrealistic at all. It just goes to show that Viraj did not feel the need to hide his real face to Jhanvi. He started his abuse of her from the first night, in a psychological way (drinking the cockroach) and that furthermore develops into a physical abuse!
And realising the craziness of her husband, she gets the guard to open up the door and makes a run for it.. only to be caught and him punishing her by burning her feet. For a girl like Jhanvii who was very lively one slap should have been enough to make her run away!
