I wonder is it because she is frightened of being alone at night wherever she is, or whether she is frightened of being alone in her own home because she has to confront the reality of the loss of her DH, and that’s always very hard if you wake up in the middle of the night? It may help her if she can change up her bedroom so that it feels different, or if she could try sleeping in another bedroom if she has one. I agree that it would be good if you could stay with her at her house for a few nights, to try to understand exactly what it is she is frightened of. Getting a dog or a cat is also a good idea, as there is another presence in the house then, which changes the way it feels.