For some strange reason, women sometimes stay with men who are absolute animals. Usually, they lose their children to social services because of it, a step which unfortunately came too late this time
Saw too many instances of that when I worked in the 'Family' courts
There is a lot of forensic investigation done in abuse cases where there's hasn't been a fatality (and so the child is usually made a ward of court and in care by then, so no jury is involved in proceedings away from the criminal court). Because it's done separately in the civil courts the hospital and other expert witnesses can give evidence to the trial Judge only which means that speculative evidence can be given which couldn't be permitted in a criminal trial but can be used to establish likelihood as to how any injuries including mental and emotional harm were caused and sometimes who would have inflicted it.
As this little girl had 'older' rib injuries than the ones that contributed to killing her I expect that the timing of those must have co-incided with time frame for the perverts having access to her for the mother NOT to be in the frame for the actual abuse. As for 'not noticing' the injuries, again these can sometimes be hard to identify, especially if they're internal, unless there's massive bruising or scratches and, sadly in neglect cases, routine hygiene is often so bad or non-existent, it does sometimes go unnoticed even by community health professionals.
As for this Koran thing - shades of Brutha's granny or wot?