Okay, it's been a while since I studied the mural image. So, I googled for one, and here's an image of the mural.

We've been assuming that's PD in the mural because we've been told Rose shattered PD, PD oversaw Earth, and the like. But looking at the coloring of the two, Rose in the mural is colored pink. The gem she's fighting is not colored pink though, and if that was Pink Diamond, I would assume she would be pink. The gem she's facing off against here is colored white. So maybe this whole time the mural was depicting Rose fighting White Diamond. The image certainly seems to have the same hairstyle that we've seen in other depictions of White Diamond (like the big statue/whatever on Homeworld).

I wonder what the precise timeline for the war thousands of years ago was. I wonder if White Diamond could have attacked and shattered Pink Diamond, and that contributed to a precipitation of Rose's turn against Homeworld. And Homeworld just put out a false line that Rose shattered PD and everyone's just bought it, including the Crystal Gems, and Rose allowed that lie to go unchallenged because she found it useful for gathering forces to help her fight against Homeworld. That would be a way to absolve Rose of PD's destruction, but still leave her behavior morally questionable.