Let’s remember that often times the title of the episode refers to more than one person, so “lost girl” could refer to Tamara and whatever her backstory is but it also obviously has to refer to Snow in FTL of the past (based on those pics that I STILL CANNOT FIND she is wearing her wedding outfit from from Lady of the Lake.)
I think HappyEndings is correct that Tamara was never in NL. A and E said at SDCC that GOAT do not know they are working for PP. I think she was born in our world to Marian. I’m starting to suspect, based on the TVLine spoiler about RH being in SB with Belle, that RH did not follow Marian through to our world 3 years before the Curse hit so that explains why he is in SB. Marian dies when Tamara is a young girl and her “grandmother” (FGM possibly?) tells Tamara that magic might have been able to save Marian but this world has no magic thus turning Tamara bitter against magic.