"Surah An-Nisa aya 11: To the male a portion to that of two females."
Women are guaranteed a right to inheritance by the Qur'an. The degree depends on how many others are involved. It may be assumed that there is injustice in the way it is done but according Islam the man is responsible for the maintenance of the woman.
As stated in the book Women in Shari'ah by 'Abdur Rahman I. Doi. page168. "the important point to be made is that female relatives both ascendant and descendent have automatic rights of inheritance when the necessary conditions apply. Grandmothers, mothers, aunts, sisters ( both full and half), daughters and granddaughters all have rights of inheritance under Islamic law thus granting to them as women a legal and economic status which was not achieved by their counterparts under European and other legal systems until very recently."
He goes into some detail on the portions allotted in various cases. He states for further details these can be gained form books on fiqh and from 'ulama, some of whom have made the subject their specialty.