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She'll be a target for the mad, sad and bad from the likes of IS and the EDL if she comes back.

I don't think she's banned? But she might not be helped to come home.
A lot of teenagers want a cause, glory and/or infamy. Thankfully most of them don't act on it (or get distracted by food/shoes/sex/music/booze until dull adulthood.)

How much blame you can attribute to her versus the many people who have been influencing her I don't know.

I can't say I'd be happy to see her at the school gate, but I'm not sure it could be considered justice to ban her from the UK either.

You can acknowledge that she is a product of the external factors / influence, while still thinking that there is a point at which you have to accept responsibility for you actions.

The reality is that she will likely be jailed and the child will end up in care.

Intellectually, the question is whether becoming a citizen of ISIS has revoked her British Citizenship? My understanding is that legally in the UK you can have dual citizenship without applying for it, therefore, there can be no restriction on her right to return, or upon returning the rights of her child.

A good analogy would be RIO pre-independence and Scotland now. Should pro-indy people have a right to English+Welsh citizenship if they support breakaway from the Union? If so, then is it specifically the violence and criminality which ends her citizenship?