Confused on a grading scale

So in engineering, the entire class did pretty bad on this recent test, with  everyone averaging a C(which is funny because we actually checked the answers and people were right when our teacher marked us wrong). So we all had to to do a makeup test,and on any retest, the highest you can get is a 79. So there were 30 questions, and I got 25 right, which is an 83. So somehow, she took 83% over 79 and managed to get a 65 out of that which is really annoying. So instead, even though I got a better score on the makeup, my original grade for my first test was still better because she graded weirdly, so I got a C.