The old saying is March comes “in like a lamb and out like a lion” … or the reverse. Since this artwork suggests Judith tore it up like a lion on the way out, she must have gone in like a lamb.
And the lamb would make sense, considering the Holofernes’ original dinner invitation. He must have thought Judith would be meek like a lamb. And even from Judith’s POV, the start of the evening is not the occasion to make a big roar and be vicious. Or rip off the host’s head.