Echidne has been writing up an excellent series on Daesh and women, including on the rules they enforce on Sunni Muslim women and their establishment of sexual slavery for non-Sunni-Muslim women (not easy to read).
Her latest installment is on women who voluntarily join ISIS/IS/Daesh/whatever and their motives, experiences, and outcomes. In my view, one of the most important takeaway points of her work is that it is not the case that the women who join and support ISIS, especially the ones coming from the West, are dupes who do not know what they are doing. While some of them end up regretting it, there are not a few of them who are ideologically committed to what they are building, and not measurably to a lesser degree than the men who join it---some of whom are also naive dupes who don't understand what they were getting into, but not all.
The reality is, the view of "mainstream" society into religious-fanatical, particularly Islamically-motivated fanatical societies and organizations is coloured by a materialistic calculation of costs and benefits which these groups, almost by definition, don't share. That women, even willing women, must accept less personal freedom than men does not register within the minds of the subjects of this discrimination as a moral assault. Quite the contrary, the distribution of clear life-roles is viewed as an obvious advantage of the Daesh dystopia. From their perspective, who wouldn't prefer the clear outlay of detailed life expectations to the chaos and confusion of "free, liberated" life in the rest of the world? For them, it must be the devil misguiding the rest of us to believe that "the search for Mr. Right" is better than having one's spouse and sex partner simply assigned.
More importantly, Echidne's post points out the obvious fact that many of the reasons that women might voluntarily join IS are (suprise!) the same reasons that men do. While this should be obvious, it is important to point it out because a lot of Western media interprets gender relations in the Muslim world as a whole through the lens of a kind of rescue fantasy. Those Muslim women who, unimaginably, aren't waiting for the American troops to roll through and liberate them from their nasty bearded husbands/fathers in favour of some unspecified life doing...what?...in the feminist utopias that Western colonies universally become can only be accommodated, in this narrative, by an imputed Stockholm Syndrome.
The case of female ISIS volunteers is a piece of evidence against the rescue narrative that is difficult to ignore. This is not in itself, however, evidence for some kind of deep relativism. However, if liberation is a basic goal, then what it is evidence for, to risk a platitude, is that such liberation cannot be effected in the absence of willing participation by the liberatees, so to speak, and when that participation is withheld, it can sometimes be withheld with knowledge of what is being rejected.