Let's see if we can review the facts about Cozy for a second.
What is Cozy Glow? Cozy Glow is a pegasus filly of roughly the same age as the Cutie Mark Crusaders.
What did Cozy Glow do? Cozy Glow nearly wiped magic from existence.
Why did Cozy Glow nearly wipe magic from existence? Cozy Glow wanted to remove magic from the world to trap the mane six in Tartarus.
Why did Cozy Glow want the mane six in Tartarus? Cozy Glow wanted them trapped in an inescapable prison so she could take command of the school of friendship.
Why did Cozy Glow want command of the school? Cozy Glow wanted to have the most friends in the world.
Why did Cozy Glow want friends? Cozy Glow wanted power.
How does having the most friends give Cozy Glow power? Friendship is the most powerful force in Equestria. Therefore, more friends equals more power.
How did Cozy Glow try to wipe magic from existence? She used six magical artifacts to attract all of the magic in Equestria then tried to send it into the void.
How was Cozy Glow's plan foiled?
The friendship student six and assistance from the Tree of Harmony allowed the artifacts to be removed, returning magic to Equestria and its residents.
What was Cozy Glow's reaction to this change? Anger, mockery and swearing vengeance.
Did Cozy Glow show remorse? No.
Did Princess Twilight Sparkle try to emotionally connect to Cozy Glow? Yes. Twice, in fact.
When did Princess Twilight Sparkle try to emotionally connect to Cozy Glow? After returning from Tartarus.
How did Princess Twilight Sparkle try to emotionally connect to Cozy Glow? She sought out Cozy Glow's motivations. Then she apologized for Cozy Glow not understanding that friendship is more
Was Cozy Glow receptive to this attempt? No.
What circumstances are similar to Cozy Glow's situation at the time of her defeat? Both Starlight Glimmer (the first time) and Queen Chrysalis refused to accept they were wrong and tried to escape.
What is a sociopath?
so·ci·o·path /ˈsōsēōˌpaTH/ noun
a person with a personality disorder manifesting itself in extreme antisocial attitudes and behavior
and a lack of conscience.
Is Cozy Glow a sociopath? While Cozy Glow has demonstrated a lack of concern for how her actions effect others, it could
be argued that her understanding of social behavior and ability to emulate it disqualifies her as a sociopath.
So, let's round this out with three loaded questions.
Would Cozy Glow be reformed? Not within the final season of the show.
Could Cozy Glow be reformed? If we are to assume Cozy Glow has a similar mentality and willingness to change like other reformed villains then yes.
Should Cozy Glow be reformed? That's not really something that can be decided without diving into a few thousand years worth of philosophy and ethics.
As things stand, Cozy Glow's age seems to be a key factor in the question of her downfall. Does her age disqualify her from punishment? Is her youth an excuse for her behavior? Is the law of Equestria absolute or would special consideration grant her amnesty? Is being stoned equivalent to a death sentence? Is there room for interpretation of what could happen next? Will the season 10 comic address these issues? Will fans accept the season 10 comics as canon?