How can I cope with my Mother?

She is 80 and has always been a bully. She had a difficult upbringing. In the last ten years our relationship improved because she was ill and needed my help: she was suffering from dementia, incontinence and immobility. I got her the medical help she needed and she made a good recovery. Now the bullying is back. It takes 3 hrs round trip to visit her and I have been spending a large part of every weekend. I feel depressed and weepy. I cannot concentrate. She wont listen to me and gets really angry when I try to talk about it. I wish I could just run away but I cannot. My brother refuses to come home.