Who's Demonia?

Who's This? A snake in the grass.

The facts: One of the original Omega Men who premiered in Green Lantern #141 (June 1981), Demonia was Harpis' sister, but also turned out to be a traitor to the cause and betrayed the group to the Citadel. She was killed by Tigorr in Omega Men #4. She appears in an extended flashback when Omega Men #11 tells Harpis' origin, and is briefly resurrected (as a Darkstar!) in the 2007 mini-series before being destroyed again.
How you could have heard of her: A minor Omega Man? The Who's Who entry is probably the apex of her visibility.
Example story: Omega Men #4 (July 1983) "Breakdown" by Roger Slifer, Keith Giffen and Mike DeCarlo
Most of Demonia's appearances were made before the Omega Men series - in GL and NTT - and as one of the original members of the time, I somehow doubt she was always tapped to become a traitor (unless it was already in her thought bubbles even then? Experts, let me know!). So let's look at the actual "turn". As that issue begins, Demonia is presented as Felicity's confidant, advising her on her love life, seeing as she used to be a beautiful exotic dancer herself.
Is that last panel suggesting Demonia is Kaa to Felicity's Mowgli? Her advice to set a jealousy trap for Tigorr is kind of on the villainous side, but just in a soap opera kind of way. It may not be necessary anyway, because Tigorr walks away from a poker game and tells Felcity "c'mere, I need a little release". Eech, why is this series so icky? (I'm sparing you elements that have nothing to do with Demonia, including a really gross body swap between a shape-shifter and Kalista.) But it seems like Demonia has been planting "seed thoughts" into many resistance members because Tigorr is soon challenging Primus for leadership. That's all just internecine conflict though, it doesn't mean she's a traitor to the cause. Unless there's more to the plan...
They fight to a standstill, as Primus refuses to his mental powers, but then Tigorr gets hit by a psychic attack, which Primus denies is his. The berzerker doesn't listen and starts ripping him to shreds. But Demonia doesn't have psionic powers! However she's doing this, she sends video to the Citadel's jumbo-tron offering them the Omega Men as a prize, if they capitalize on the team's instability right now. They don't have a big window, because Tigorr figures out that Demonia gave psychic agonizers to some of the rebels and he goes out looking for her. So it's tiger vs. snake:
And unlike Tigorr's fight with Primus, this one isn't nearly as long.
Yep, that's it. And Demonia's reason for betraying the group? Entirely philosophical? Abstract "inner demons"? I don't get it and I don't buy it. She doesn't even have a deal with the Citadel, isn't asking for anything in return, and her reasons for revenge as thin at best. She just gives in to her perceived role as a literal "snake in the grass". Perhaps there's more to it in full context, but this issue itself doesn't give it. I also resent the killing of the character absent her sister Harpis who you'd think would have something to say/feel about this.

If this is all they had in the tank for this character, it's probably better that they kill her off early.

Who's Next? A master torturer.