I would never let an IS member (man or woman) back into normal Western society. I wouldn't be able to trust them regardless of what change of heart they may claim to have.
This is a large part of the reason why the problem won't be solved. There are just under 30,000 ISIS fighters. Many members of ISIS are not fighters - like these girls - and instead fill various other roles, from support personnel (ansar), security forces (hisba), trainee recruits, and so on. In total, there are probably about 200,000 ISIS associates in Iraq and Syria. To put it another way, that's the population of Aberdeen, Scotland.
It's not practical to kill or imprison that many people on mass. Firstly, just having the troop numbers to not only deal with 30,000 active ISIS fighters, but also the full remaining 170,000, is a struggle for Syrian and Iraqi forces at the best of times. Sending in outside actors could make the situation better, but would require very careful handling. If the handling is the United States says "let's kill/imprison every single person associated with ISIS", that doesn't make the situation better.
It makes it worse in four key ways. Firstly, the moment you tell your opponent there will be no quarter, they will fight like there is no quarter. Bribes and amnesties have typically been much more effective at destabilizing extremist and criminal organizations - for a recent example, see Abu Sayyaf in the Philippines. Secondly, you risk large civilian casualties. At the point there are 200,000 people who have been to integrate into the local civilian infrastructure, and you have a 'no quarter' policy, then it's very, very difficult to ensure that local people don't occasionally end up at the wrong end of that policy - much more difficult than when you take a softly softly approach. That's exactly the sort of thing that results in locals being more likely to join ISIS, turn against outside actors, and make the problem worse by turning the situation from what is currently fairly typical warfare to guerilla warfare proper. Thirdly, you risk making martyrs of members of a religous organization where the lowest ranks have very strong convicitions in these religious ideals, or at least at the point where they join. Fourthly, you damage the capacity of actors in the area to gather good information about ISIS when you discourage ISIS members from defecting. A great deal of Western intelligence about ISIS comes from Sweden, and that's because Sweden has a rehabilitation policy that makes defection a reasonable prospect when you realize how awful ISIS is - something a lot of recruits either don't realize or don't really believe.
If the West wants to deal properly with ISIS, it has to accept that a reasonable rehabilitation process for some if not all members is the only practical way to do it. When the Allies entered Germany after the war, they didn't execute every single person ever who had even been remotely associated with the Nazis. That would have been an absolutely horrific policy that would have condemned Germany to failed state status for decades into the future. Instead, they undertook a deNazification policy aimed at making people realize, regret and reintegrate. This is we need to proceed with ISIS.
