What is the inheritance share of a wife who did not bear children from her husband, if he dies and he has a sister and a mother, or only a sister?

What affects the inheritance of one spouse is the presence or absence of offspring from the deceased, not the presence of the mother or sister. So, for someone who dies and leaves no inheritable offspring, his wife receives one-quarter, based on Allah's saying: ﴿And for them [wives] is one-fourth of what you leave if you have no child.﴾ If he has inheritable offspring, his wife receives one-eighth, based on Allah's saying: ﴿But if you have a child, then for them [wives] is one-eighth of what you leave.﴾ Inheritable offspring include: a son or a daughter, or a son's son however low he may be, or a son's daughter however low her father may be through male lineage.

Therefore, for the woman mentioned, if her husband has inheritable offspring from another (marriage), she receives one-eighth; and if he has no inheritable offspring, she receives one-quarter.

It must be noted that matters of inheritance are serious and complex, and a mere fatwa is not sufficient. Rather, it must be referred to the Sharia courts for investigation, as there might be other heirs, or wills, or debts that take precedence over the rights of the heirs.