If Diana was still a baby when that happened I can see Hippolyta waiting until she was old enough. But I'm fine with Diana knowing from the beginning as well.
I don't think keeping them as twins will dilute Diana's importance. I do like the idea of Phillipus co-creating her and essentially making her the daughter of Hippolyta and Phillipus but kidnapped when she was young. It adds more layers to Nubia's origin while also elevating Phillipus's importance. Bonus points, if you reveal that Phillipus is Nubian and that she named her daughter after her old home land.
Yep. I remember that thread but I recall agreeing with her at the time but that was before Tumblr really took and it was on there that Nubia went viral and I started changing my mind about the character.