>>42699292
Cozy Glow was manipulated and groomed by Tirek, she wasn't 100% bad on her own. Plus we don't even know anything about her home life or lack thereof. Could be she's normally as mean as Diamond Tiara, who is a bully but not pure evil. Also,
>>42693851 (OP)
looks like the face of someone who's only just realized the weight and magnitude of their actions, but knows it's too late. And before you respond with an image of the three blowing up Canterlot, I want you to at least consider the next paragraph.
Tirek and Chrysalis acted as stand-in parental figures, giving her a sense of belonging. Children don't start out with a well developed sense of right and wrong, they follow what the authority figures in their life expect of them.
Stygian and Tempest got off light. Cozy Glow should face some amount of punishment, that does not involve Tartarus or permanent encasement in stone.