Yes, I understand that you used DE, it was in your posts. Unfortunately, DE will not be that effective against and infestation. Your hen had Nits (Lice egg) attached to her feathers, so a sprinkling of DE in the dust bathing area is not going to get rid of the parasites.
When you can, I do...
I'm sorry about your hen.
Hard to know why she died without necropsy, there's so many things that can happen.
Since you did find lice on the body and I do see lice nits on the feathers, I'd recommend that you go ahead and treat the rest of your chickens and their housing to get on top of any...