Is it permissible for a woman observing the 'iddah (waiting period) due to her husband's death to move from the house of 'iddah to another house to complete her 'iddah, if her psychological state necessitates it?

The fundamental principle is that a woman whose husband has died must observe her iddah (waiting period) in the marital home and should not leave it except for a valid excuse, based on the hadith of Furay'ah bint Malik. The majority of jurists, both from early and later generations, have adopted this view. However, if she experiences psychological distress, or finds it necessary to leave, such as fearing for her safety or property, or suffering severe harm from neighbors, then it is permissible for her to move. If your mother is experiencing the aforementioned difficulties, then there is no blame upon her for moving.