Velvet is practically a Devil in Plain Sight, acting kind and sweet in public, but being a horrible, manipulative monster to anyone she gets alone, to the point where it's amazing she's able to mantain the facade at all.
Justified: Velvet has a position or family life which requires a high amount of charisma or a constant facade of amiability. Since she can never appropriately express negative emotions or opinions, they come out in inappropriate or exaggeratedly abusive mannerisms.
Zig Zagged: Velvet is a very nice and friendly person in public, but a Jerkass in private...but it turns out that she is still a fundamentally good person, just a bit rougher...however, that turns out to be yet another layer, and she's a manipulative villain underneath...except she's Affably Evil.
Velvet is exactly as nice as she appears and no one ever even hints otherwise.
Enforced: "Crap, the audience wants Angelo with Jennifer, but we can't just kill Velvet off. I know! Let's 'reveal' that she's actually been pure evil underneath all along and just pretending to be sweet! It couldn't possibly fail!"
Lampshaded: "I should have known you were a bitch. All pretty flowers do is distract from razor thorns."
Invoked: Velvet knows that her personality won't get her any allies, so she starts trying her hardest to seem sweet, though she never denies her inner personality.
Angelo personally investigates everyone he comes into contact with to ensure he won't be fooled by a pleasant act.
Angelo calls Velvet out for only pretending to be nice, and convinces her to drop the "sweet" act entirely.
Discussed: "Keep an eye on that one; there's no way she's that sweet."
Conversed: "Sure, she seems sweet, but she's a) the most popular girl in school and b) dating the main character's love interest. Odds are good it's just an act hiding one sick bitch."
Once Velvet drops the facade in front of somebody, word spreads and her mask is permanently fractured, until her sweet persona has completely crumbled in the face of utter disbelief.
The heroes are taken in by her, and disdain the rough diamondNature Hero, resulting in disaster. And they're still not seeing through Velvet, because she is still charming, so they blame the Nature Hero.
Aware that her reputation could be ruined by word getting out, Velvet takes steps to ensure nobody who sees her darker side will ever be able to warn anyone.
The Nature Hero sets out and forms a new team, seeking out less powerful characters with better judgment, who can solve the problem.
Played For Laughs:
Velvet literally turns into a snarling, drooling monster the second everyone but Angelo aren't paying attention. Of course, nobody believes his babbling about her horrible alter-ego.
Alternatively, the character Angelo, hurt by Velvet, sets her up with the even worse character Charlie. Velvet proceeds to get her just desserts to Angelo's amusement.
Played For Drama:
Velvet lures Angelo into an abusive relationship, then plays the Wounded Gazelle Gambit when he tries to tell others, leaving everyone hating him and rallying around her for support.
Again, Angelo is hurt by Velvet and he sets her up with the worse character Charlie. Velvet gets her just desserts and more. It becomes so bad that Velvet is emotionally and/or physically abused much worse than she abused people. Even when she repents she is still stuck with Charlie. Bonus points if Angelo refuses to help.