Yeah, that's something often glossed over too. She's actually self-righteous enough to forgive the killer as if she has the right. Because she's so self-centered and bratty, it's all about her and how he broke the promise with her, not the actual death or destruction.
And immediately after, she's lying to her beloved master's face and justifying it as "for a friend".
Hopefully, even if she isn't killed for it here, they'll just throw her out and let her join the demon side as an enemy in the future.