Since she's locked up in the hospital I've been wondering if Dr. Hopper is actually treating her and that maybe he will somehow become aware of who she is through his interactions with Mr. Gold when he begins treating him. Not necessarily their FTL history together – I don't think that Gold is going to talk about the fact he is Rumple and was in love with Belle, but if he talks about a woman he loved who died . . .who knows – Archie might put it together and figure out that the woman in the hospital he had been treating is the woman Gold thought was dead. He isn't too keen on Regina anymore so he might figure out that she was involved in her being locked up in the first place.
You are a genius! I absolutely LOVE this idea. It definitely could happen.