As a family member we don't know anything about my sister's medication

My sister is involuntarily hospitalized in a hospital in NY, and as her younger brother, I contacted the hospital asked them to talk with the doctor, but the doctor refused to share any information with me as she ( the patient) didn’t sign any document to release her information with me.
Though married, my sister is not a good understanding with her husband and he is indifferent towards her situation. After her hospitalization, i talked with her couple of times and she is still angry and delusional and refused to sign any paper.
What should I do now? As i am really worried about her and don’t even know about her diagnosis and medication. Any help or suggestion is much appreciated.

You really won’t be able to get much information about your sister’s treatment unless she signs a release of information paper for you. I know it feels dreadful, sorry you have to deal with this worry. The one thing you can do is try to find a sympathetic staff person on your sister’s unit. They also cannot tell you anything specific about your sister, but there is nothing restricting you from sharing any information with them that they might find helpful.

Let your sister know you care, and let the staff know you would like her to sign release, and at some point she might come around to it. You might use some kind of incentive with her if there is something she would like to have in the hospital that you could bring to her, on condition that she signs the release. I know that sounds controlling, but it could be helpful.