Is it obligatory to wash all long hair completely with every ghusl from janabah, despite the difficulty and repetition?

A woman is not required to undo her hair when performing ghusl (ritual bath) after major ritual impurity (janabah). It is sufficient for her to pour water over her head three handfuls until it reaches the roots of her hair. However, if her hair is braided so tightly that she fears water may not reach its roots, then she must undo it. The Prophet, peace and blessings be upon him, was asked about this, and he answered Umm Salamah, may Allah be pleased with her, by saying: "No, it is sufficient for you to pour over your head three handfuls, then you pour water over your body, and you will be purified." This is what the scholars have agreed upon, with a few rare exceptions. As for the ghusl after menstruation, there is a different detail which includes rubbing the head and ensuring water reaches all parts of it.