If a psychiatrist suffered a mental breakdown and had to be committed, she'd hardly be committed to the same hospital she worked in. Particularly when it's a hospital for the criminally insane, with inmates/patients who no doubt harbour grudges against her.
When Miranda wakes up in a cell after her murderous blackout, Pete (Robert Downey, Jr.'s character) tells her that he pulled some strings to have her placed under his supervision. Otherwise, she would have ended up in another institution.
Even if he thinks they could treat her better under their care or that she needs familiar faces, it's still not a good idea to put her in general population with her own previous patients.