Let me start on a positive.

[indent][list][*]I agree that Kelnorahs personality section was left rather bare on my part. I believe I was simply trying to focus that not much is [b]known[/b] about her in this world. I can certainly expand on it.[/*]
[*]Being that the parents will be PCs, I can also go back and emphasize more on Nora/MC interactions and/or simply Nora.[/*][/list][/indent]

[b][i]HOWEVER[/i][/b]
I also feel the need to rebuttal on some of your points.
[indent][list][*]Yes. Kelnorah and Nora are vastly different. Kelnorah is portrayed as a prankster and "messes with people for the sake of it". This is exactly as you say. Just because Nora is seemingly perfect, does not mean that the MC sees her as such. I was trying to build up the impression that the MC sees Nora as a rival of sorts, someone who is always doing things to undermine her. "Oh look. Another good grade. I swear she only does that to make my average grades look worse." Or "another sports trophy. Now my medal for participation in X sport seems to be nothing!"[/*]
[*]Yes, this is a big assumption but, that is what I was going for. I find it a little difficult to build my supporting character for a MC that we still know very little about. So, it is troublesome to become specific without determining something about the character that is not within my control.[/*]
[*]Plus, I thought we were to all have an "equal stake in changing the way the main character behaves, what her backstory is and how she will grow through the experience", as mentioned in the OP. My character simply shows that she has a jealous/envious relationship with her older sister.[/*]
[*]Also, in terms of Kelnorahs character, though she may be a prankster, her "growth/maturity" role is for the MC to come to terms with having the cancer, just as Nora was trying to do in the real world. This is why I had given her the "Brutally Honest" trait. She may play some childish prank, and say the MC has a chose of two items, the one she chooses causes some comical outcome, say dying her hair some outrageous color. Kelnorah would swing by and say something along the lines of "You can't keep blaming others for what is out of their control."[/*] [/list][/indent]

--END RANT--

I'm still interested in participating in this RP and, as stated, I will adjust as best as I can to your criticism. However, the shell of my characters will be essentially the same. If you do not like this and would rather I drop, I will do so without qualm. 

Regardless of decision, I wish this RP success and hope I can be a part of that.