There is no difference between half or full brother/sister in the matter of inheritance distribution. If one has no children, one’s brothers and sisters will inherit him – whether they are full or half maternal/paternal brothers and sisters. In other words, Step brothers/ sisters will only inherit from their real Father, Mother, Brother and/ or Sister.
In this particular case, after payment of outstanding debts of the deceased and after fulfilling the will of the deceased, half of the remainig inheritance will go to the step-sister. There will still be un-distributed amount in this case. In case the deceased does not nominate anyone whom this remaining inheritance should be distributed (which can be the same step-sister as well), then it can be distributed to the nearest male relative as per ijtihad of Prophet Muhammad (sws) (Sahih Muslim no 3929) in accordance with Quran 4:11 اَقْرَبُ نَفْعا (the closest in benefit).
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Law of Inheritance in Detail:
Discussion 10380