Total BS from your lib friend. Plus Indian tribes did not go to war that often against each other over hunting grounds. More often it was for successful braves to accumulate more honor-prestige. For young braves to make their bones. For braves to capture other tribes women and turn them onto baby factories and sex playmates.
One aspect of prevailing over other tribes was to have greater numbers. So capturing women and having them produce children for your clan and tribe is a good strategy
Captured women commonly endured a period of slavery, often at the hands of the other women. Those who could not hack it remained slaves. Those who could, were often permitted to marry into the tribe and gain status. At the mercy of those who might see them as competitors for desirable men, the captured might be disfigured by those in control of them to take them out of the running.
Captured women, screened thus, added, via their children, to the gene pool. Slave women's children might not fare so well.
As far as producing children, well, all the women were pretty much expected to. It was a way to replace those lost to disease, hunger, and warfare.
As far as the women being the torture experts, that is no surprise. Women have a general capacity for vindictive acts far beyond what most men would exact. Men would just kill the SOB at some point and get on with the rest of their day.