Is it permissible for the mother of the husband, who is observing the 'iddah (waiting period) after her husband's death, to stay overnight in her son's house (not the marital home), and is it permissible for her to visit her husband's grave before the 'iddah ends?

A woman observing 'iddah (waiting period) after her husband's death is not permitted to spend the night outside her home except in cases of necessity, such as fearing to spend the night alone, in which case she may move and spend the night with her son. However, visiting her husband's grave before the completion of her 'iddah is not permissible.