@Zakir, you here? The reason i asked you for reference was to know whether she immediately becomes free or after the death of her master...what does your sources say?
I got it from a article on this website called does Islam allow the rape of female slaves I think it was by karim it says :
"But as it aimed at putting an end to such issue, Islam laid down rules which would eventually lead to eradicating the practice. So it allowed Muslims to have intercourse with slave women taken as captives of just and legitimate wars. In so doing, the woman would automatically become free if she got pregnant. What's more, her child would also become free. "