How can one perform ghusl for prayer when there is a headache that worsens with ghusl from janabah?

Water must reach the skin and the roots of the hair when washing the head after major ritual impurity (janabah). However, if it is proven that washing her head harms a woman, based on her experience or a doctor's advice, she is permitted to wipe it instead of washing it, for there is no hardship in religion, and it does not burden one with what is beyond capacity.