Migration law ruled Rau case

If the authorities believe one is an illegal migrant, but the doctors believe the person is mentally ill, what does the law say?
a) Put the person under migration detention, or
b) Put the person in a mental health clinic

The Townsville Bulletin reports Migration law ruled Rau case:

"IMMIGRATION authorities detained mentally ill Australian Cornelia Rau in solitary confinement for eight weeks, under a detention policy that demands that migration law take priority over doctors' advice."

Why such a ridiculous law? Well, A lot of long-term detainees develop mental illness, and this is the only way the government can keep the damage the government has been doing to other human beings out-of-sight of the general public.