It isn't Fred. Hermione cries over Fred, she mourns him, she loves him, but he isn't enough. She'll feel guilty about that later, she'll make amends, but right now, it's Colin. Little Colin Creevey is being carried into the Great Hall by Oliver Wood, and it breaks her. He should never have been here. He should never have died for them. He's a child. She's not Halfrek, but she looked after children too. He's one of her's, and she failed him.
She's Hermione Granger, so she goes to the library. No one notices her leave.
The library is empty and surprisingly untouched by the battle. Hermione goes straight to the Restricted Section. It takes her less than a second to break through the protections meant to keep out students, not a teenage witch who spent eleven hundred years as a vengeance demon, and then she takes it all. She drinks in the knowledge and the power in all that ink and blood-used-as-ink and it burns like fiendfyre because the human body is not supposed to hold this much power. It's the kind of power that makes witches burn kingdoms and try to end the world. Good thing that's exactly what she's planning on doing.
She flies on wings of darkness and, for the first time in seven years, she is vengeance.
The Death Eaters are considerate enough to come to her. She hovers above the destroyed courtyard and there is silence. Then she spots Hagrid with Harry in his arms, Harry pale and unmoving, and the power rises out of her with a shriek. An entire wing of Death Eaters turns to dust, but there is only one monster who could have killed the boy she half considers her bother.
"Tom Marvolo Riddle, face me!" she yells. "Face me and die!"
The red-eyed worm below her lets out a high-pitched laugh, heedless of the demise of his servants. "You dare threaten Lord Voldemort? Avada Kedavra!"
The green light is absorbed by the cloak of shadows Hermione surrounds herself with. She tilts her head to one side. "I see no Lord."
She throws the worm's own killing curse back at him, and the battle begins. It ends when she rips the bones from his body and throws them to land with the head of the snake she finds out later that Neville has killed. The Death Eaters would be an afterthought, like crushing a bug beneath her shoe. They hurt children. They killed children. They will not live.
"Hermione!" an impossible voice calls. Impossible because she saw his body, she saw him dead. Still, she turns towards it and she sees Harry, whole and alive, cutting down fleeing Death Eaters to reach her.
She collapses into her friend's arms and weeps.