Lola's mother? The lips in the flag kind of remind me of it and Nami could be with her.
Big Mom being Lola's mother has been a theory before we even knew her name (just going from how Lola's crew talk about her massively powerful mother in the New World, her being an Emperor seemed likely), and only looks more and more probable since then.
But yeah, not sure if she actually is anywhere near Fishman Island.
You are a Rose, You are a blade
I'm Down on my knees in the dark and fiery reign
-David Defeis, Virgin Steele