She was thinking of when Harry finally broke down and told her the truth.
"I'm not just some loose end, a victim that got away! I'm not just a thorn in Voldermort's side! I'm the only one that's capable of killing him, or vanquishing him for good! The entire world IS resting on my shoulders!" he screamed at her.
"Why do you think that?" she asked through her sobs, eyes full of tears. She had pushed and pushed, she wasn't going to stop now, not until he finally told her what was bothering him. She knew she was close.
"That bloody prophecy!"
"Prophecy? I thought it was destroyed?"
"That was just a fucking recording! Dumbledore told me it AFTER Sirius died! Wanna know what it says?! 'THE ONE WITH THE POWER TO VANQUISH THE DARK LORD APPROACHES... BORN TO THOSE WHO HAVE THRICE DEFIED HIM, BORN AS THE SEVENTH MONTH DIES.... AND THE DARK LORD WILL MARK HIM AS HIS EQUAL, BUT HE WILL HAVE POWER THE DARK LORD KNOWS NOT... AND EITHER MUST DIE AT THE HAND OF THE OTHER FOR NEITHER CAN LIVE WHILE THE OTHER SURVIVES...'!"
Suddenly she remembered something Harry said about magic "I've learned that magic is all about will. All you have to do is want something bad enough and it will happen. Wands and incantations are just a means to focus the will." She wasn't gonna let a little thing like prophecy stand in her way. She would kill Voldermort herself for taking her Harry away from her.
Hermione stood and held her palm toward the Headmaster. "Sorry Professor, but I need your power - obscurum tribuo mihi vox."
The surprised look on his face was only surpassed by the one on Ron's, as a bright light moved from Dumbledore's chest to Hermione hand. Dumbledore's limp body slumped onto his desk.
"Wh- wha- what did you do?" Ron gasped.
She whirled on Ron and glared at him. He tried to back away but couldn't.
"OUT OF MY WAY!" she screamed and the chair he was sitting on flew across the room with him still on it.
Hermione stormed towards the door, leaving the room crackling with energy. As she walked determinedly towards Griffyndor tower, she could feel herself draw the energy from all around her. The suits of armor fell silent and fell apart. The paintings stopped moving. Anyone that saw her in the hall quickly headed the other way.
She had to blow her way through the Fat Lady. She entered the common room to complete silence and scared looks from the few students around. She stomped her way up to the boy's dorm. The door opened before she got to it. Only Neville was inside and he quickly scrambled out when he saw her with the door slamming behind him.
She quickly moved to Harry's trunk and opened it. She pulled his quidditch robes, Firebolt and invisibility cloak out. She threw her nightclothes off and started to put his quidditch robes on. As she did, they shrunk to fit her and their hue turned a deep green, barely distinguishable from black, and hardened. She grabbed the invisibility cloak and put it around her shoulders and watched as it melded into the armor. She turned to face the mirror and take in her new outfit. Her eyes glowed a fierce black. She willed her hair to a jet black that reminded her of Harry's. An evil smile crossed her face as she appraised her new look. She grabbed the broomstick and watched as her form shimmered and disappeared in the mirror.