nurse has been accused of stomping her 92-year-old grandmother to death because she thought she was possessed by demons.Rachel Armstrong is alleged to have thrown her grandmother Angela Armstrong down a flight of stairs at the home they shared.The 37-year-old then stomped on her repeatedly breaking her arm and eight ribs.Armstrong told police in St Louis, Missouri, she believed her grandmother was "a demon" or possessed by one.She told investigators she wanted to beat the demon out of her grandmother's body before putting her to bed.The elderly woman died in hospital almost a month after the November 11th attack.Prosecutors had initially charged Armstrong with assault on an elderly person now plan to bring a manslaughter charge.After Armstrong's arrest last month, police took her to a hospital for a psychiatric evaluation.