My top five might be:
Circe (she's short next to Aphrodite, but I think she has substance; and as I've said before, you've loved her so long, she really should be on your backup list. Circe feels very specific to me, too.)
Ginevra (I'm liking this lately, and I like the fact that this form distances you a little from King Arthur's Guinevere. Is she a little...normal?...next to Aphrodite, though?)
Isolde (Very pretty, very tragic, yet substantial too. I like the culture contrast between Aphrodite and Isolde, and the E-endings give them a suitably subtle link.)
Zenobia (This has never been one of my favorites from your lists; I just don't care for the sound, I think. But it seems to have staying power for you, and it does have the sparkle and the substance to stand up to Aphrodite. I also like the A and Z, though not sure where you'd go from there--B and Y? :))
Best wishes! I'll add suggestions if I think of any.
I like Isolde, Zorya, Sybilla, Olympia, and Calliope.
I really dislike: Nausicaa, Cleopatra, and Nefertiti (The last two are way, way too tied to historical figures--I don't think they would really suit a child well. Despite Nefertiti being awesome. If you must use them I'd put them in a middle spot)
This is only somewhat on topic, but I seem to recall that you removed Gwenllian because it's difficult to pronounce for Italians, correct?
If that's the case and you're on the fence about it, I should mention that I've taken Spanish immersion classes since I was little, and although my various Spanish teachers could never say the G with the W, I was fine with answering to [vague phlegm sound]-wen.
And this is all relevant because Spanish is close to Italian. Kinda. The point is that I don't think the pronunciation issue by itself is a good enough reason to ditch Gwenllian if you really like it. And I feel like Winnie would be even easier to pronounce.
Also, if you're on the fence about Pandora and need to be persuaded, I'm prepared to defend it. With catapults and boiling oil and everything.
And while I really like Proserpina and think it's woefully underused, part of me is hesitant about it because it doesn't feel as brave as your other choices.