She isn't mad at the start.
I didn't use the word "mad". I find that word to be less than helpful, as it usually refers to literary depictions of mental illness that aren't very similar to reality.
I said, "prone to mental illness". This is a woman who has been sexually abused by her brother, effectively kept in (admittedly pleasant) captivity, and sold into marriage. Her brother is brutally murdered before her eyes, iirc, and then she is taken on her wedding night in a way that hardly speaks "loving and informed consent".
If you want to think she's a well-balanced individual, who wields bloody violent power in a thoughtful, empathetic manner after all that, you are free to do so.