Is it obligatory for my sister to wear the legal hijab at the age of 13, knowing that she wore it at the age of nine, then she was required to remove it at school due to her poor eyesight?

A girl must wear the hijab upon reaching puberty. It is recommended for her to be modest [or covered] when she reaches ten years of age, to accustom her to modesty and because she might be desired at this age. Weak eyesight can be treated with shaded glasses while adhering to the niqab; there is no need to uncover the face. The preponderant opinion is that covering the face is obligatory.