Why is there so much vomiting with someone with end stage cirrhosis? is it due to fluid pressure in abdomen, causing pressure on stomach? or something worse?

Worrisome: Cirrhosis leads to major changes in the ability of the body to handle any stress. Repeated vomiting is not a sign of cirrhosis in of itself. Seek attention urgently as real trouble may ensue quickly.

Not very common: but not unusual. Ascites compresses the stomach and pushes it further into the chest, enlarged liver/spleen can also shift the abdominal contents. many medications can be nauseating. would try to control the ascites to the extent possible, if that's not the issue - discuss further with the hepatologist.