Without thinking, Draco pulled his wand as his parents were focused on the emaciated girl on their floor. He cast the modified protego that he and Theo had designed. They'd been using it all year to help protect the students being tortured at Hogwarts without detection. It's not much, but no irreversible nerve or internal damage would be sustained. Hopefully her brilliant mind would stay intact, but he’d never used this spell against one of Bellatrix's victims. 