How can I help my mother handle seeing my brother, her former verbal and emotional abuser?

My parents are both in their late 80s. My father has long standing vascular dementia from multiple TIAs, Parkinson's, and paranoid personality disorder. My brother alienated my father from my mother (his wife of 60+years) and other siblings and then started verbally abusing my mother when she would not agree to sign deeds. It escalated to the point where he blocked her in a corner, stood over her yelling (he's nearly a foot taller), and told her she couldn't leave the corner until she signed the checks or insurance papers like he told her too. Mom would call her other children and sometimes the police to come rescue her from my brother. She could not throw him out because my father would always state he wanted him there.

According to my brother, the only problem is my mother doesn't "mind" well enough and other siblings are sticking their nose in. When he filed for conservatorship, asking to set aside her POA choices (a different sibling and I), she moved in with me and was found competent. Mom has MCI and her short term memory is pretty bad but she decided a couple of decades back that she never wanted my brother having any say in her affairs. Plan has always been for Mom to move in with me after my father died (his health has generally been worse than hers) and the situation with my brother only made that happen sooner. Mom appears very content living with me, doctor agrees getting out of the stressful environment has helped her a lot. She is back to her "normal" self again (not the stressed out version of the past few years), reads books, takes walks, socializes when we go out or someone comes in, does some chores around the house because she wants to be useful, interacts and plays with the great grandchildren that are around almost daily.

There's only one real problem. My brother demanded to talk with my mother after she moved in. I would inform my mother my brother was on the line wanting to talk with her (with the phone down where he could hear the question and answer) and she would state she had nothing to say to him (she was very angry with him over trying to gain conservatorship). One day my brother shows up at house demanding to talk with Mom. I tell him through the door he needs to leave. He sees Mom through the window and walks up to the window, knocks on it, then uses his finger to gesture she needs to come to him while he yells "come out here right now". He wouldn't leave until I had called the sheriff's office. The lawyer I used in fighting the conservatorship called his lawyer and brother hasn't been back. Since this incident more than a year ago Mom has what I can only call anxiety episodes whenever my brother is around or she thinks he might be. We live next door to another family member and my brother visits there occasionally - every month or so. He doesn't try to approach my home, but Mom can see him from my house. While my brother is around and sometimes for days afterwards, she checks that the doors are locked every few minutes, cannot read or watch TV without getting up and checking out the windows, doesn't sleep well at night, etc. I tell her that he's not going to come back down to the house and bother us, that the doors are locked and he can't get in, that we can call the sheriff again if I'm wrong and he does head our way.

What else can I do to help her?