Does a doctor's order supersede a POA?

My sister suffers from mental illness and my mother got POA yesterday. My sister was in ICU after a suicide attempt. Her current psychiatrist will not be taking her back so a social worker in the hospital assigned her a new one. The psychiatrist has been seeing my sister for two days and she says he makes her uncomfortable and he will not give my mother (who has POA) and information and saying that all the decisions are his to make because she is his patient. My mother wants to transfer her to a better hospital and obviously a different doctor but the psychiatrist says his doctor's orders supersedes my mother's POA and we'll have to get a lawyer and go to court in order to change that.