Drusilla had done it again.
She'd been told, time and time again, not to attract attention to them when she could avoid it. And, time and again, she failed to properly dispose of the bodies of her victims - sometimes even deliberately left them to be found before the group left town!
Darla didn't know why Angelus insisted on keeping the girl around. But since he did, and he was apparently unable to keep her under control, it would have to fall to Darla to mete out discipline.
"Drusilla! You've been naughty, haven't you? Bedroom. Now."
She ignored the girl's excitement.