What is the ruling on trimming the ends of hair by a specific woman whose hand is believed to be "blessed" and helps to thicken and lengthen hair?

The belief that cutting hair by a specific person makes it grow longer and thicker is baseless. Blessings are from Allah Almighty; they are not affirmed in anything except with proof. They mean an abundance of goodness, its increase, or its permanence. Seeking blessings (Al-Tabarruk) is a matter of divine instruction (tawqifiyyah), so it is not permissible except with what is supported by evidence. It can be in time, like Laylat al-Qadr (the Night of Decree); in place, like the three mosques; in things, like Zamzam water; in deeds, for every righteous deed is blessed; and in persons, like the Prophets themselves. As for the blessing of those other than the Prophets, it is a blessing of action, not an inherent one that transfers. It is not permissible to believe that a person possesses blessing.