Is it permissible not to oblige a sister who has reached eleven years of age to wear the abaya, and to suffice with alerting her to men, or to oblige her with an abaya with sleeves and a niqab due to her weak eyesight and the difficulty of the regular abaya for her?

An adult woman must veil herself from foreign men with the legal (Shar'i) dress that conceals her adornments and does not reveal any of her body parts. The Shar'i abaya is one that achieves complete concealment, is thick and not clingy, covers the entire body and is loose, is open only from the front with narrow sleeves, is free from adornment and resemblance to the clothing of disbelieving women or men, and is placed over the head. An abaya with sleeves is permissible if it is concealing and unadorned. The niqab is permissible if its opening is only for the eyes and does not reveal any part of the face, especially when there is a need for it.