All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
Any Muslim girl who has reached the age where she has her menstruation period should wear the Hijab (a garment that covers the whole body) that covers her from being looked at by alien (i.e., marriageable) men because it is at this age that the girl becomes addressed by the orders of the Sharee’ah and should abide by them. Allaah Says (what means): {O Prophet, tell your wives and your daughters and the women of the believers to draw their cloaks (veils) all-over their bodies. That will be better, that they should be known (as free respectable woman) so as not to be harassed. And Allaah is Ever oft-forgiving, Most Merciful.}[Quran: 33:59]
Allaah Knows best.