Impa in SS is most definetly diffrent then OoT Impa, shes simply a guardian the gods have placed to help Link and the royal family, first she never really manipulates time, the gate of time only moves between those two time periods i believe, so she did not time travel to OoT, two she dies, or now that everthing is at peace, leaves to were she truly belongs at her age, last just because they look simeler does not make them the same, thats like a theory a little awhile ago by someone i forgot whos name is that Termina is the land of the ocean king just because they are partily similer does not make them the same, i believe many Zelda theoryist aim to call two items people or places the same, sometimes it may be true, but alout of times not.