All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
No doubt, parents get a great reward from Allah for raising their children. Taking care of their physical needs and their health is the responsibility of parents. So, they have to look after their children’s physical health so they will grow healthy, especially the disabled ones.
In fact, this is the job Allah has charged parents with. The Prophet said: “Everyone of you is a guardian and everyone of you is responsible for his subjects.” [Al-Bukhari and Muslim]
It is also the responsibility of parents to raise their children according to the Sharee'ah, teaching them the religion and good character in order to become a continuous source of good reward even after their death. The Prophet said: “When a person dies all his good deeds cease except for three: a continuous act of charity, beneficial knowledge, and a righteous son who prays for him.” [Muslim and others]
Therefore, the questioning sister may know that there is a good reward in raising such a child.
Allah knows best.