Is it permissible for a mother observing the 'iddah (waiting period) after the death of her husband to appear before her daughter's husband?

A woman observing the 'iddah (waiting period) after her husband's death must stay in the home where he died for four months and ten days. She should not leave it except out of necessity or dire need. She should treat her daughter's husband as a mahram (unmarriageable kin). Thus, it is permissible for her to sit with him, converse with him, and uncover her face and hands in front of him, and so on, because the daughter's husband is a mahram to her mother, as stated in the verse: (and mothers of your wives). She is permitted to live her normal life in her home without undue hardship; she may cook, bathe, converse with whomever she wishes, and shake hands with her mahrams and with women.