@Mr. Power perhaps I missed this part, how did she help with the Red Wedding?
All I know is she could not keep Joffrey in check at all when Tyrion could, allowed Joffrey to behead Ned and start a two-front war. She is awful with PR as all of the poor hate her, and her doing nothing to address that was part of the King's landing riot (meanwhile Margary puts on PR for the poor). She also had plans to have the wildfire launched from inside the city, which very easily could have turned into a disaster when a mistake was made.