There are three possibilities that I can foresee based on what little we have so far. I don’t think we are looking at an alternate universe or some other rupture in the space-time continuum.
1) Perhaps it is possible Jennifer is playing a character other than Emma.
2) The boundary bet. the world of SB and the EF is breaking down.
3) Everyone goes back to the EF for some reason.
Side note: Jen’s costume is very similar to the one Lana wore in 2×10 another connection bet. the Regina and Emma may be in the works.
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Custodian of Graham's darts, Rumple's spindle and Robin's quiver