Aww, Zia Amara is such a beautiful name! Personally, I'd go with "Zia" as the main one since it's short and sweet na, pero a few of us mums use both names when we want to sound fancy or when they're in trouble, haha. Some of my friends with longer names do "Zi" or "Zimi" if they want something extra playful, or you could go "Mara" from Amara if you want to switch it up, honestly, nicknames usually develop naturally as she grows, so don't stress too much about picking the "perfect" one right now!