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.
Undoubtedly, it is better and safer to have your brothers' wives, the wives of your friends, a female Mahram of yours or any Mahram of this girl's to advise her to abide by the commandments of Allaah and His Messenger .
However, there is no harm in sending her some useful booklets and tapes. Still, beware of Satan lest he drags you to directly talk with her with the pretext of calling her to Allaah. This is an evil temptation of the accursed Satan and a plot he weaves against you.
Allaah Knows best.