I'm on the other side of the table, so I'll give you my perspective. You should get valid feedback from your prof, because you're supposed to be able to use that to improve. That's not optional, and it's not negotiable. However, hearing someone whine about their grade is entirely different. In her opinion, you did C- work, and that's what she gave you. The discussion is about what you do to improve, not that you deserved a better grade. You have another twist on this, since it's an online course, so I don't know if that means a face-to-face meeting is even possible. You'd probably get more info from her via e-mail. I'm assuming she uses turnitin? If so, didn't she give you feedback on your paper? Comments and the like.
Two other thoughts. First, I don't know which school you go to, but going up the ladder is most likely going to be useless at most institutions, especially if it's a Research 1 university. What you can do is nail her on her evaluations at the end of the term (you do get to do those, I'm assuming). That gives her feedback, gives her bosses feedback, and if she's up for tenure, it goes in her file.
The second thing is that before you take a class, you may want to look up your future profs on ratemyprofessors.com. It's incredibly invalid, because anyone can post anything on there, yet it seems to be remarkably accurate nonetheless. Do your fellow students a favor, and go there and post a review of this woman. They'll know to dodge her classes.