Is the Hajj of a woman accepted if she performed Hajj at the age of 14 with other women, accompanied by the husband of one of her sisters who is not a mahram to her, and she was unaware of the necessity of a mahram for Hajj, or is she required to repeat the Hajj?

Her Hajj is valid despite her committing a prohibited act by traveling without a mahram. If she was ignorant, she is excused and must seek Allah's forgiveness. If she was aware, she must repent and seek Allah's forgiveness. As for its sufficiency for the Hajj of Islam, if she was an adult at that time, her Hajj is sufficient. If she was not an adult, she must perform Hajj again, and her first Hajj is considered a supererogatory act.