Is the speaker responsible for the accidental death of her brother, after he choked on the rice she offered him?

There is no sin upon you, nor is there any liability, because placing food after it is fit for consumption is permissible. And whoever does what is permissible for them Islamically, and harm arises from their action, then there is no liability upon them, as in the jurisprudential maxim: "Permissibility under Islamic law negates liability."