Is it valid to perform ghusl from janabah and permissible to pray if not all of the hair is washed, and only a portion of it is washed, and what should one do whose hair falls out when washing it daily?

The entire body must be covered with water during ghusl al-janabah (ritual bath for major impurity), including washing all hair on the head and ensuring water reaches its roots, regardless of whether the hair is thin or thick. Normal hair shedding does not permit neglecting to wash the head. However, if the hair loss is severe and disfigurement is feared, and its cause is washing, either by experience or through the information from a trustworthy doctor, then it is permissible for the woman to wipe over the hair that she fears damaging by washing, and she should wash what she does not fear damaging. This is because jurists have considered the fear of losing an organ or its function as an excuse for tayammum (dry ablution), and this applies to the current situation.