I've kept both of mine, but I never combine my black dupes. Or most of my plat non-event dupes. I should note that I don't have Olivie though.

I rarely use the second one, but maybe way down the line, you might want to skill AW one Sybilla and keep the other one regular AW'd in the rare situation that you'd need an assassinating princess?

Or have both skill AW'd, if you want.