I wonder if she got beaten often due to being angry, and that was how she met her end.
That was my thought too, Longtom.
People who knew her said that physically she was a big, strong girl - though she would still not have anywhere near the strength of a man like EC - and I suspect that they underfed and brutalised her to keep her physically weak, and to stop her from leaving (and taking her allowances with her). They might even have told her her dad don't want her anymore - there's nothing (as far as I am aware) that indicates that she knew he was dead.
I think she was largely locked in that horrible room and left. Just left alone, day in day out - fed and toileted sporadically, when they could be bothered, and that she either died there of neglect, or EC lost his temper with her (perhaps she was crying or begging to get out) and beat her just once too often, and just a bit too hard.
Poor, lonely soul - she must have been so frightened and unhappy. Just awful.