Hi there! If her writing is error focused it means that her writing would be focused specifically on avoiding errors. If you are not feeling yourself it means that you are not feeling good. It can mean both mentally and physically. We can also use the phrase he/she isn't himself/herself today. This phrase is often used to describe someones behaviour, if someone is not behaving the way they usually do because they are feeling sad or not normal mentally or physically for some reason: 'John isn't himself today. He is usually very talkative but today he seems very quiet, I wonder if something is wrong.' Hope this helps, let me know if you have any questions!