Yes, I think Regina has a backstory before Daniel that we have never seen. I think she knew Robin before she ever met Daniel. I think Robin gave her the green ring. I think her and Robin’s memories were wiped and they do not know that they knew each other before. This parallels the story of David and Mary Margaret in Storybrooke. They had a relationship, David gave her the green ring, they had a baby and they didn’t remember any of it at all. Mary Margaret makes the comment, “Snow White had a kid…you would think she would remember that.” We also saw this in the Enchanted Forest when Snow White drank the potion and wiped her memories of Charming.