I believe Chanel number 3's earmuffs are radio devices and she has something - or everything - to do with the killings even if she is not the Red Devil herself, which she just could be.
She is IN the bathtub in the intro that randomly showed up in episode 5.
Denise and Hester only tell the ghost stories to people in the room so it had to have been transmitted to the Red Devil by means of a telecommunication device given that everyone who heard it was already in the room Denise ran into after the toilet paper incident with the Red Devil. Chanel number 3's earmuffs could be in place to transmit intel.
She also tries to sit out the blood oath claiming she has HPV. It is also only the girls present in the room that hear Ariana (Chanel#2) saying she is going to her room, and perhaps whoever was listening to what Chanel#3's headphones transmitted.
She is seen taking a black phone case out when the Chanels discover #2 dead. Also, it was in her pocket as if she'd just had it.. Just like she did when she was killing #2 a few minutes ago, if she was the red devil that day.
Perhaps she refused to hook up with Sam given that she was aware they were being overheard constantly.
She is always aware of the dead bodies being kept in the fridge room and she could be providing intel to the devil so he, if not she herself, could take it away. She was also alone in the kitchen before the fryer instead when Chanel#2 went up to search for a "bigger bowl" and saw the creepy collage in the maid's room.
She is the last person to see predatory lez (Sam) alive and kills her, perhaps in a cold attempt to retain the emotionless dedication to seeking revenge, just like she does when she kills Boone if at all that is her.
We don't even know her real name yet. She was the last one to be seen with the shovel in episode 2, so perhaps she deliberately left the shed door open for herself or for the other red devil to get the lawn mower later at night.
With Chanel#2 out of the way for trying to escape/ threating to "call her mom", Chanel#3 is next in line to be Kappa President. This is also why she may have bailed Chanel, to stop Chanel #5 and #6 from conspiring a plan that ended with Hester becoming President. This could also be why she quickly flat out admits to plotting to kill Chanel when accused of doing so by Chanel herself in episode 7 in which she, Hester and Chanel#5 plan it together with minimum inputs from her. How she had Ariana Grande/ Chanel#2 show up in Chanel's dream? Perhaps she just drugged her and then went and whispered in her ears. Or even wore Chanel#2's clothes given that she claims to have taken them (It's what she says to #2 at her funeral.) She also does not seem displeased with Chanel's plan to kill Hester in e9 the way Chanel#5 is.
She claims her father is Charles Manson, who is in jail, and yet she claims it is him (her father) who wires her money to bail Chanel when she is arrested. It is improbable that it's true Charles Manson is her father, perhaps it's just random stuff she was brainwashed into believing because why the heck would her mom be allowed to visit him in jail? She also casually mentions in the canteen that she joined Kappa for a sense of identity that she lacked otherwise. She has a tattoo that says 8/69. I don't know what this may mean. I read somewhere that this could be a reference to the Sharon Tate murders carried out by the Manson family.
If she spent the previous summer away from the Kappa house, she could have been with Melanie Dorkess whom she saved in the red devil costume after the acid spray tan incident. Remember, we see Melanie fall to the ground but not die. Instead, she sees the Red Devil in front of her.
She has never been attacked by the Red Devil yet and she has only been seen without her earmuffs twice, once in her first scene in the pilot and the other time when Denise is introduced to them. I'm not sure why these 2 days were specifically picked out as her day "off", but oh, well.
Also, she hasn't been attacked by the red devil so far. Then again, neither has Grace. And the Red Devil found Mandy and killed her only after Grace and Pete visited her caravan in the woods but it might not be them, they could have been stalked.
I like Chanel#3 so much, though so I hope Grace or maybe even Wes has a personality disorder or something and is responsible for everything.
I also find it dubious that Pete and Wes have been absent for the most part, and that Pete's former obsession with Chanel has not been explored.
RIP Boonie ily