Is it permissible to cut the hair of a Muslim girl who works for me and give it to my sister, who suffers from thin hair, for the purpose of attaching it to increase the density of her hair?

It is forbidden for a Muslim woman to attach other hair to her hair, even if it belongs to another Muslim woman, due to the generality of the authentic hadiths that prohibit this. Among them is the saying of the Prophet, peace and blessings be upon him: "Allah has cursed the woman who attaches hair [to another's hair] and the one to whom hair is attached, and the woman who plucks eyebrows and the one whose eyebrows are plucked."