The boggart wasn't reacting well, she could see through her tears of laughter, and much more of this would finish it off. But she couldn't resist - if she just added some kind of ludicrous veil to the whole ensemble... gasping and practically doubled over with laughter, Corrie raised her wand enough to laugh out, "R-r-riddikulus!"
There was heat, and light, and sound. Sharp pain in her hand and a sudden sense of loss - and the feel of rushing backward very quickly and out of control, hair sweeping up and forward to block her view, but not for long. She felt herself crash painfully into something, and then she fell to the ground, hurt and lacking and too dazed even to try to make sense of what had just happened.