Ibn Umar (may Allah be pleased with them both) says, concerning a woman in the state of ihram, that she should cut an amount of her hair equal to the index finger. And it is reported from Sayyidah Aishah (may Allah be pleased with her): We used to perform Hajj and Umrah, and we would not cut more than a finger's length.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 9407