How is it clear that the woman was herself in a very abusive relationship?
Just because that is the line of defence her lawyer is using doesn't mean it was actually the case. And even if it was, how does that excuse her not protecting her own children?
We want to believe she was so cowed and frightened that she was somehow brainwashed into accepting the situation because it's alien to us to imagine that a woman could ever wantonly facilitate or turn a blind eye to the abuse of her own children, but the simple fact is that some women just do. Does it always have to be that women are deemed as so weak, so helpless, so stupid and so easily intimidated that they are incapable of protecting their own children from the men they are in relationships with?
If you don't feel able to stand up to your own abuser that's one thing, but when you are a mother it's your job to stand up to those who would abuse your children, irrespective of whatever you are personally going through. If you know they are being abused and you don't take reasonable steps to put a stop to it then you simply have to be held accountable.