Is prayer and fasting obligatory for a mature girl with Down syndrome, and should she be trained on that, knowing that her mental age is less than her actual age?

Mongolism is a disease that affects children in their mothers' wombs, causing mental and physical retardation. Its signs include prominent and swollen eyes, a drooping lower lip, and a yellowish complexion. The affected individual may also make involuntary movements, may not be able to control their urine and feces, and can mimic and imitate but does not understand the true nature of things. The person afflicted with this condition is exempt from religious obligations; thus, they are not obligated to perform prayers, fast, or fulfill any other religious duties. However, training them in whatever obligations are possible is a good thing.