but beside the heinous nature of her crimes, her actions negate societal norms.
This is an excellent set up for the arguments of your essay. After this, you should describe what societal norms Medea's actions negate, and why and how.
You might organize your essay this way: for example, making the first paragraph 1) about how Medea's story negates the traditional social norm of the obedient wife, then making the second paragraph 2) about how Medea's story negates the traditional social norm of the loving mother, etc.