Corrie slapped the boggart as hard as she could with her left hand, so hard the sound rang, so hard it stung her. So hard the flashlight went flying and they were once again in darkness. But she drew her wand anyway and cast a stunning spell in the direction where she'd knocked her semidoppleganger. "I'm already turning it around," she snarled, spinning in place - had the spell hit? It was impossible to tell in the darkness. There was a footstep to her left, and - "Stupefy!" Corrie said, then gasped at the sudden heat, and the pain in her fingers. Don't drop the wand, don't drop the wand, she thought, gripping it tighter, and turned toward the sound of the boggart laughing. "I don't bloody need you to... Stupefy!" she said again, and this time there wasn't the familiar zing or even heat, but when she stepped forward again the floor was slick - she had to grab the bedpost to stay upright. "Stupefy!" she said again, and it was only her instincts that saved her from being smashed by something huge and heavy she'd accidentally summoned her way.
The boggart's laughter was as good as an I-told-you-so, and Corrie stood there panting angrily for a moment before growling, "Bloodywellfinethen, lumos!"
The room came suddenly into view, so bright she had to squint to see the boggart, and Lorcan still on the bed, and the dresser halfway through the wall behind where she'd been standing.