Yeah, that initially bugged me, too. That Taris and Toreth weren't the same person. According to official sources, the writers thought that Taris died, which is BS, since the episode heavily implies that she and her ship are going to survive.
Usually on a TV show, the producers will opt not to have the character be the same, since then you have to give the original writers a fee for the re-use of a character they created and it can also mean an actor pay bump for playing a "recurring" character.
One could also argue that perhaps Toreth might recognize Troi, though that would be a bit of a stretch.
Heck, at least Taris had decent hair, before the TNG staffers decided that every single Vulcan and Romulan character should have the exactly same utterly awful hairpieces which looked painted on. It was amazing how bad those hairpieces became in later seasons and how much better they were earlier. WTF?
