In her human form, Chelsea looks as much of a human as anyone else, while in their human forms, the Gillmans nevertheless still look like blue blob beings, so of course Chelsea had it easier fitting with people in one day than Ruby ever did in her life.
The song used in Chelsea's reveal as Nerissa, is "Pink Venom" by BLACKPINK. The contradiction theme of the song best fits her confident yet dangerous personality and her sweetheart facade.
Chelsea, who is actually an adult masquerading as a teenager, was completely fine with all of the teenagers at Oceanside High going crazy over her, and even responded the sentiment back to one claiming to love her (and wanting to marry her).
Since mermaids don't age, this means the krakens waged war with and slaughtered a race of teenage girls as well as forced the remaining members into hiding (as confirmed by Word of God) in fear of a continued genocide.
Director's commentary confirmed Chelsea could have really felt sympathy for Ruby's plight explaining the infamous scenes where she does genuinely seemed concerned. If so, that would mean mermaids are capable of feeling empathy for those not like them which by definition would no longer make them inherently pure evil as Grandmamah and Agatha would suggest. Combine that with them feeling fear, it makes Grandmamah's desire to have them all killed feel even less justifiable.
