Is my professor being unfair?
When lecturers mark the worksheets / assignments, they try to assess student's knowledge and understanding of the subject. Of course, they can not look inside the student's head, so they have to make judgement based on what they see. Mark schemes and rubrics are introduced for the sake of objectivity and consistency, particularly when several lecturers share the marking. However, we have to accept that no mark scheme and rubric can cover absolutely everything. There are always some distinctions between students' works which are not accounted for in the mark scheme, but still (by a lecturer's judgement) should be accounted in the grade. That's what she probably tried to explain to you when you asked. 

It is impossible to tell from the fragments you show if your work is really of the same quality as you peer's or not. We can't tell by just looking on your graphs --- something essential may be written in the comments above and below. To me it looks like these two papers are both wrong in some aspect, but I am not sure these errors are "equivalent".

You professor backed up a little by offering you an extra mark. It is hard to tell, if you really convinced you that she's been unfair, or she just don't want to spend her life arguing about it. It may well be that she deviated from the rigid set of criteria prescribed by the mark scheme, but I would not blame this on her personally. The mark scheme is not the law, in a sense that it is probably not more important than your professor's expert academic judgement. I can see a point in your frustration, but it really looks to me just as a manifestation of the complex nature of academic assessments in general, not as her bias against you.