Before they took the children to Azoth House, Severia changed into clothes that wouldn't hinder her in combat, including a pair of sturdy boots, and she had grabbed a dagger - an ancestral relic that she hoped wouldn't dissolve in a shower of rust as soon as she unsheathed it - as well as her wand. They had left the children and Nanny Stella with Serenus and picked up Tybalt before setting off for the Ministry.
She had no idea what they would find when they arrived, but a roomful of ghosts wasn't it. She could feel magic in the air, thick and almost oppressive, and it flowed into her, as if seeking any available receptacle.
She spotted Gaius and Regulus with Potter and Black, but before she could suggest joining them, her attention was distracted by the entrance of Crabbe. Not her former student, but his equally thick-witted parent. No doubt Crabbe had felt the call, and he was lumbering toward the Veil with a look of dumb reverence, much like Bellatrix's own.
"Stop him! We need to keep her isolated. She's dangerous enough without allies!"
Remus and Tybalt raised their wands and shouted "Stupefy!" at the same time she did, and she was stunned by the sheer force of the energy behind their spells; after weeks of thin streams, suddenly they had a flood at their disposal.
Crabbe went down, felled by three potent stunning spells, and Severia nodded with grim satisfaction. He wouldn't be getting up again any time soon.