Lady Death's preferred fighting stance
Given that she's in basically the exact same pose, and how often Lady Death is just generally in boobs and butt poses, I can only assume this is actually her preferred fighting stance.
Maybe she's trying to get a Steam achievement like "Kill 100 enemies while thrusting your butt out toward them."
(Covers of Lady Death: Origins Annual #1, Boundless Comics & Lady Death: Dead Rising #1, Avatar Press)