Is it permissible for a mother in her iddah (66 years old) to travel from Egypt to Saudi Arabia to stay with her daughter and perform 'Umrah, considering that the daughter will return with her to Egypt in October to resume her work, or must the daughter leave her work and stay with her mother until the iddah period ends?

A woman whose husband has died must observe mourning (ihdad) for the duration of her 'iddah (definition) (waiting period). She is not permitted to move from the house in which she received the news of her husband's death, as was established in the hadith (definition) of Furay'ah bint Malik. Therefore, your mother is not permitted to travel or perform 'Umrah (definition) before her 'iddah has concluded. As for you, you are permitted to travel to her with a mahram (definition) (unmarriageable kin) and with your husband's permission, and this is commendable and preferred.