I don't care how cute she's acting now, I don't trust her or like her. She killed her friends, maimed them, etc., etc. I feel like Hussie is sort of making excuses. She did things recently which, for me, place her in the entirely irredeemable pile.
It's not a matter of Vriska "being cute" all of the sudden. I'm rooting for her because, out of a cast of characters who have mostly served as vehicles to tell jokes, she's taken decisive action in the plot and has developed a lot as a character. It probably doesn't help that she's a misguided but well-intentioned trickster, which is among my favorite heroic archetypes.
I agree that she's done absolutely reprehensible things through the story, but as opposed to the cardboard cutout villainy of Jack or Eridan (I am homicidal because I have been programmed to hate/lack self esteem, respectively), she means well by it, has shown regret for her actions several times, and when confronted with the reality of her past seeks to change tack. She's competent and badassed, but instead of the godlike untouchability of Dave, she has been known to trip up and pay for it (in lost trust, friendship, and even lives).
Vriska is a dynamic character who manages to simultaneously be
funny and terrifying, and
sympathetic while reprehensible. I certainly don't think she's trustworthy (not unless she proved her intentions with some appropriate actions), but she's definitely one of the most self-aware characters in the cast, and surpasses John in having come the farthest as a character.
To conclude my Spiderspiel, I don't think anyone is beyond redemption so long as they are aware of the gravity of their past actions, and honestly work to change their ways.