I was unsure at the time how to read her sudden sympathy for the creep that was possibly looking to rape her, but your comment gives my a theory:

I think this scene to highlight the contrast in how the actual Shoshanna reacts to the consequences of her violence and how her ghostly projected image reacts. While the physical Shoshanna shows real concern for the individual life she’s just taken, the cinematic Shoshanna laughs maniacally at the mass slaughter she’s responsible for.

And what’s important is that both of these contradictory reactions can come from the same person, and both can be perfectly justified! True, Zoller was a little shit, but at the same time he was a real person who Shoshanna always seemed more begrudgingly bemused by than truly disgusted with. Zoller was both responsible for death on a massive scale and sickened by having to watch them celebrated. Shoshanna can be both justified in killing him and remorseful about having had to do it.

Similarly, it’s possible as movie-goers to get visceral thrills out of watching Nazis get their comeuppance in brutal, brutal ways, while simultaneously feeling bad about the drunken German’s freshly orphaned newborn. Just because the reactions are contradictory doesn’t mean you can’t have both. In fact, I think most of the climax is about how the different players are reacting to violence (either on the screen, or in the theater) and how those reactions mirror the different feelings we’ve just experienced over the past couple hours.