I do think that probably as time went on (well, I guess not really) she may have gotten “comfortable” with time standing still and fell into a pattern of being large and in charge as mayor of Storybrooke and Henry’s mother; just gotten used to the curse working.
And then Emma showed up and suddenly Regina has to face the facts that the curse isn’t going to go exactly as she has planned. I think Rumple was just sitting tight waiting for Emma to show up on 28th birthday – there wasn’t any reason for him to confront Regina or let on that he remembered because nothing was going to start to happen until Emma showed up and he knew that.