What is required is to cut the hair following Hajj or ‘Umrah, taking from all parts of the head. For more information please see the answer to question no. 110804
If it is not possible to take from all parts of the hair, because the hair is layered, then the woman should gather her hair and cut something from the ends.
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) was asked: Some women have layered hair, as they call it, and it is not like braids from which the length of a fingertip may be cut. How can they cut from all over the head?
He replied: It should be cut from each layer.
Then I asked him: But it is not possible to tell the layers apart.
He said: In that case it is sufficient to take from the ends.
End quote from Thamaraat at-Tadween.