Provide students a checklist or a rubrics on common errors: Give them a check list that details common problems. Students can run through each item when doing their final proof-reading.
Make a list of common errors: Having accumulated all the example mistakes, she can start compiling a list of common errors. That piece of notes can be itself a teaching material, and also a comment code. When grading, for instance, she can then refer to "RO" for run-on sentences, or a numerical code #14. Students can check the acronym or number against their common list of mistakes, and figure out what went wrong. She can also augment the list of common errors with common corrections as well.
Last year, I modified the approach (I teach epidemiology, so a bit different than arts). Instead of using the historic list, I listed the mistakes of the very same group of students. On each student's work, they will see a random ID code at the top of their paper, and some mistake codes along the passage. Then, on the mistake list, I put the problematic part next to the student's random ID code, and then categorized it under the type of mistakes. That way, students can figure out what are the mistakes, and they can also learn from all others' mistakes.
Use MS Word's track change or Adobe's commenting capabilities: Most of the time I wasted was to find space to scribble my comments and corrections. I went paperless for about 1.5 year and apart from saving paper, I've also saved a lot of frustration with scribbling by shifting to using track change (for docx files) and online commenting (for pdf files) for grading and correction. Other then comments, I also put links to reference websites (in your girl friend's case, online text book or dictionary.)