Is a sick girl held accountable for not performing her religious obligations and fasting? Is she allowed to refuse marriage and childbirth for fear that her children will not be able to worship?

The sick person is advised to be patient and to frequently supplicate and implore Allah for healing, to perform Ruqyah Ash-Shar'iyyah (Islamic incantation), and to engage in the remembrance of Allah.

Obligatory duties do not cease for a sick person as long as they are conscious. They must perform these duties. They are permitted to avail themselves of the concessions of Sharia, such as combining prayers and breaking the fast in Ramadan if the illness permits it. They must make up for missed fasts if the illness is expected to be cured, or feed the poor if the illness is chronic.

As for someone who is not conscious, they are not held accountable, and there is no sin upon them.

Regarding refraining from marriage or procreation due to a hereditary disease, if a trustworthy doctor states that the disease will be transmitted to the children, then there is no objection to refraining from marriage, as marriage is not obligatory unless there is a fear of committing fornication.