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 is His slave and Messenger.
Yes, it is permissible to marry this girl and you will be rewarded for doing so if you intend to keep her chaste. However, the consent of the guardian is a condition for the validity of the marriage, so this marriage should be conducted with the consent of her guardian if she has a Muslim guardian. However, in case she has no Muslim guardian, then a Muslim judge –if any –would marry her off, otherwise a person who acts in his place, like the president of an Islamic centre, or his deputy, or the Imaam of the mosque; this is of course in countries where there are no Muslim judges. For more benefit, please refer to Fataawa 86524 and 83629.
Furthermore, you should be keen on teaching her her religious matters and obliging her to wear Hijab and avoid being in seclusion with non-Mahram men and whatever is a cause of temptation.
As regards the rape, if she is forced, then she is not sinful because being forced renders one not accountable. Even if we presume that she was not forced, then Islam wipes out the previous sins as informed by the Prophet . Since she embraced Islam, then her sin is forgiven, Allaah willing, as we clarified in Fataawa 86230 and 83259.
Allaah Knows best.