Even if Snow’s reaction was one of recognition, that doesn’t necessarily mean she has to have actually been there.
Maybe back in the day, she met Ariel, either in human or mermaid form, but either way, if Ariel’s originally from NL but was living in FTL at the time, she could have told Snow about it, maybe even told her what a dangerous place it is.
Or, as many have speculated, perhaps Snow had contact with Tink, and through her could have some knowledge of NL.
[adrotate group="5"]