Sayyiduna Ali, Sayyiduna Abdullah and Sayyiduna Zayd bin Thabit (may Allah be pleased with them) used to assign the wala' to the senior among the 'asabah, and among women only those inherited the wala' who had done the freeing, or (the wala' of) one freed by someone they had freed.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الولاء / 21511