Imam al-Shafi'i (may Allah have mercy on him) reported that we said: When a Magian accepts Islam, and a man's daughter is also his wife, or his sister is also his mother, we look at the stronger of the two kinships and make her inherit by it, and we drop the other; the stronger of the two is the one more firmly established in every case. So when she is both a mother and a sister, we make her inherit as a mother, because the mother remains established in every case while the sister may lapse. All their shares follow these positions in the same way. And some people said: I would make her inherit from both aspects together.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الفرائض / 12506