To Allah belongs what He takes, and to Him belongs what He gives, and for everything He sets a specific term. So she should have patience and seek the reward from Allah

Usāmah ibn Zayd (may Allah be pleased with him) recounts that one of the daughters of the Prophet (may Allah's peace and blessings be upon him) sent him a message that her son was dying and asked that he comes over. The Prophet (may Allah's peace and blessings be upon him) told the messenger to tell her to have patience and to hope for the reward from Allah; meaning that she should be patient with this calamity while expecting the reward for her patience from Allah. Some people are patient but they do not hope for the reward. If they are patient and intend with their patience that Allah give them reward for it, then this is the meaning of Ihtisāb (expecting the reward from Allah). The Prophet's words "to Allah belongs what He takes and to Him belongs what He gives" is a great statement indeed. If everything belongs to Allah, then if He takes something from you, it is His, and if He gives you something, it is also His. So, how could you be angry and discontent if He takes from you what is originally His? That is why it is an act of Sunnah that when a person is afflicted with calamity he should say: "To Allah we belong, and to Him we shall return!" This expression clearly means that we are the property of Allah, Who thus can do what He wills with His property. Likewise are the things we love; if Allah takes them from us, they are ultimately His. So, He is the ultimate owner of what He takes and what He gives. Yo do not own what Allah gives you and, therefore, you cannot dispose of what He has given you except in the way He permitted. Our ownership of what Allah gives us is limited, and we do not have absolute freedom in disposing of it. If this is the case, then how can we be impatient and intolerant when Allah, the absolute Owner, takes back what belongs to Him? This contradicts reason and text (the Quran and Sunnah). The Prophet (may Allah's peace and blessings be upon him) added that everything has an appointed term with Allah; meaning that He has a fixed time limit for everything. So, if you believe with certainty that to Allah belongs what He takes and to Him belongs what He gives and that He has fixed an appointed term for everything, you will be convinced without doubt that man cannot change the decreed term of anything, neither by advancing its time nor by delaying it. This conforms with the saying of Allah, the Exalted: {For every nation is a (specified) term. When their time has come, then they will not remain behind an hour, nor will they precede (it)} [Sūrat Yunus: 49]. So if a matter is predetermined by Allah and will neither be advanced or delayed from its appointed time, there is no benefit in impatience and discontent. Even if you are impatient and discontent, you will not change any part of fate. When the Prophet's daughter insisted that he goes to her, he went along with some of his Companions. He arrived when her child was in the throes of death. This made the eyes of the Prophet (may Allah's peace and blessings be upon him) filled with tears. Sa‘d ibn ‘Ubādah thought that the Prophet was crying out of impatience, so the Prophet told him that he cries out of mercy for the little dying boy, not out of impatience and discontent with fate. Then he added that Allah is merciful to those of His slaves who are merciful to others. This Hadīth indicates the permissibility of crying out of mercy for those who are afflicted with misfortune.