Minerva wanted to scream. She wanted to bellow and cry and lash out with every bit of pent up anger she had stored up against the man since Dumbledore's death. Instead, she coolly parried all of Severus' questions with some of her own, hoping to Merlin that Severus didn't walk into Potter under the invisibility cloak beside her.
"Have you seen Harry Potter, Minerva? Because if you have, I must insist—"*
Severus was too close.
Minerva slashed her wand in the air, hoping Potter would take the hint and run while she distracted Severus. She knew she should have expected retaliation from Severus, but was nonetheless surprised with the force of his shield charm and she teetered off balance.
Minerva was furious. Dumbledore had trusted this man—she had trusted him! She had taught Severus as a boy, had awarded him house points for good behavior and taken house points for bad.
Minerva's wand seemed to act of its own accord as she whipped a rope of fire through the air.
When Severus had first joined the staff at Hogwarts, it was she who had trusted him first. It was she who had, despite the House rivalry, formed a respectful friendship with him. She and Severus were leaders amongst the other professors—Dumbledore's first and second lieutenants.
Her rope of fire was now a black snake. Minerva caught Severus' gaze and with a flick of her wand, the snake dissolved in a swirl of heavy black smoke.
He killed Albus. After all that Dumbledore had done for him, after he had forgiven him for his sins, after he had defended him in court, after he had given him a job when no one else would have touched the Death Eater scum…
Severus killed Dumbledore.
Minerva's rage was uncontrollable. She could feel her blood pulsing under her old, wrinkled skin. She could hear her rage rushing in her ears. She would kill him; she would lose all control and kill Severus Snape.
With an angry swish of her wand, the smoke leftover from the snake transformed into daggers. Minerva's eyes met Severus' once again and cold hatred filled every muscle; it fueled the jabbing motion of her wand as the daggers aimed for Severus' chest.
There was the painful sound of metal scratching against metal as Severus hid behind a suit of armor. Minerva raised her wand again; unthinkable spells forming in her mind when Filius' high pitched voice came from behind her. It sounded distant to her and Minerva hesitated. Filius was saying something, yelling something about murder.
Minerva's wand trembled in her hand as she watched the suit of armor reach for Severus. She was no murderer.
Severus escaped the suit of armor and ran into an empty classroom. Minerva ran after him, wand at the ready, but Severus cast a fleeting glance back at her and jumped out the window.
"Coward! COWARD!"** She cried, rushing towards the window sill, anger hurtling back towards her as she watched Severus fly away.
Minerva wanted to scream. Severus hadn't even had the courage to fight back. Minerva wanted to jump after him, hex him into oblivion, make him tell her that her respect had not been poorly placed, that he had been on their side all along, that Dumbledore wasn't really dead, that this was all a bad dream…
Minerva willed herself to stop shaking as she turned and saw the other Heads, Potter, and Lovegood looking at her expectantly. Composure started to seep back into Minerva's veins—her duty as Dumbledore's first lieutenant returned.
Responsibility for those around her gave Minerva the strength to form a plan and give Pomona and Filius their orders. Minerva's eyes met Horace's worried face coldly. Here was another Slytherin colleague. Someone, who despite his bumbling, was a worthy potions maker and respectable man. With every ounce of composure left in her, she heard herself telling him—"We duel to kill."***
* Pg 598 Harry Potter and the Deathly Hallows--US Edition
**Pg 599 DH--US ed.
***Pg 602 DH--US ed.