Suffering from mental disorder.

My brother is recently married. The girl with whom she got married is suffering from mental disorder. She keeps on mumbling occasionally. She has a delusion that her own mother wants to kill her. She has a low intelligence level and remains confused regarding simple question such as her date of birth. She is inattentive most of time. She spends lot of time inside bathroom. Inside kitchen she takes 30 minutes to complete task which normally takes 5 minutes. She has a tendency of sudden forgetfulness or inattention due to which she makes danger mistakes like touching hot pan. The worst problem my brother is facing is that she don't want to have physical relationship with him. She loves him, holds his hand , hugs him but don't want to have intimate physical sexual relationship and behave awkward when asked for it like mumbling. Her parents told that she also has hallucinations of hearing voices and sometimes make awkward faces while looking at empty places as if she is looking something.