A:
If it is confirmed that
your daughter died due to drinking the fuel, and if her sister was Mukallaf (a person meeting the conditions to be held legally accountable for their actions) at that time, she has to offer Kaffarah (expiation) for involuntary manslaughter for leaving the fuel container in the reach of her young sister. The Kaffarah is to free a believing slave; if she cannot find or afford one, she has to observe Sawm (Fasting) for two full consecutive months. She also has to make Tawbah (repentance to Allah) for this. If she was not Mukallaf at the time, there is no Kaffarah due from her.