Because it is the one time that we see Calvin revealed as a person, as a human being, as a woman. In every other story, she is presented as being absolutely cold and calculating, always right and if other people would just listen to her, everything would be fine.
But here, her spirits are temporarily lifted with the thoughts and hopes of love, only to have them smashed to pieces. She states in at least one of the Robot stories that she likes robots better than humans because they are dependable, reliable companions to Man; they represent the best of us. And part of that is in general honesty and not hurting people.
For once, it wasn't someone else being hurt, it was Calvin herself being hurt. She of all people, who implicitly trusted robots because she knew them so well, who was always right, who would not, could not allow herself to feel anything like that fondness for robots for a fellow human being. And all of it fell down around her ears; her self-assurance, her self esteem, her trust, everything. Because a robot had lied to her and everybody around her, it was destroying all of the humans, doing the one thing that no robot should ever do. If it were to be copied or released to the rest of the world, who knew the damage it could achieve?
Perhaps that was the justification that allowed her to do what she did. But there was absolutely a sense of personal satisfaction and vengeance in her actions as well, for all that he had hurt her in ways that she had never been hurt, never allowed herself to be hurt, before.
Edit: I'd also add, it was one of the rare instances where she realized that she was flat-out wrong. When she figured it all out, she realized that she should have figured it out before, so she's also angry at herself.