I thought of a few other things in the live chat just now.
Some points to think about:
#1) This is definitely BEFORE Regina tries out the curse for the first time, because Rumple isn’t imprisoned yet for her to have to visit him there.
#2) Belle is about same age as Snow so this didn’t happen before Snow was born. It had to happen at some point when Snow was this age. Now, remember the episode where Snow meets Rumple? Rumple talks about love being a disease and her wanting to forget (although he obviously chooses not to himself) and we all thought he was referencing his wife but he had to be referencing Belle! That helps a lot with the timeline if I’m right.
#3) Regina talks about true love’s kiss breaking any curse. So could it be that she knows that from experience with Snow? Maybe. Or maybe not because Snow eats the apple AFTER she takes Rumple’s potion, which, like I said, I think is AFTER he met and lost Belle.
#4) Also, I think it’s interesting to note that the EQ is concerned with a mermaid rather than Snow White OR the curse because she eventually becomes obsessed with those things but she didn’t seem to be in this episode. (Unless Ariel is part of her quest. But all she said was that the mermaid was being annoying somehow…)