Through out the season from the start to now, people has basically ruled out the fact that Chanel is the killer because she doesn´t have enough motive that we can consider her the killer + the whole series basically revolves around her.
I have always thought that Chanel was innocent, but I think that she has a deeper backstory than we think. I think that Chanel is lying about her past and about her being super gross rich. I think that she is coming from a normal family (or something). And when she started college she pledges Kappa, and soon become one of Melanies slaves. And while Melanie is the president, Melanie treates Chanel as crap, which pushes Chanel over the edge. Chanel soon wants to take revenge on Melanie and basically take over her life. Chanel gets Chanel#2, Chanel#3, Chanel#4 and Chanel#5 (maybe because they all feel victimized by Melanie?) on her plan on taking down Melanie, and then they put hydrochloric acid in Melanies spraytan who eather harms her or kill her. But anyway, Chanel´s plan worked, and soon she took over as Kappa Kappa Tau president and take over all of Melanies belonging. She then gets all the Chanel´s on the plan of pretending that she is super gross rich. In the newest episode it got revealed that the college was open for visitors the day Melanie was killed/harmed, which means that everyone could be the red devil.
And in the photos of the last episode we see that Chanel, Chanel#3 and Chanel#5 is arrested, maybe because of the sabotage against Melanie?
(Btw, this isn´t a "who´s the red devil theory", it´s a theory on Chanel´s backstory".