Since she traveled to a distant world and returned at relativistic speed, time should have appeared to slow down from the point of view of someone in the inertial reference frame. (i.e. In mission control's frame, Ellie's clock should have appeared to be running more slowly than how Ellie perceived it). SR says that the respective clocks in the movie should have been the other way around, but in any case the story works better the way they did it, even though it is not consistent with SR time dilation.

Well, since she was travelling through 'tunnels' and to distant locations (e.g., Vega system and near the center of some galaxy - Milky Way?), time dilation doesn't necessarily apply. In fact, one could argue that she wasn't in the same frame as the earth bound observers once she dropped 'into' the wormhole. If it was a different frame from the earth bound observer, and the distance that separated them was outside both of each other's light cone, then my understanding is that there simultaneity of each other's frame need not remain intact. That is, my understanding - as poor as it is - is that Ellie is free to experience 18 hours in tunnel time (or Vega time, or center of galaxy time) while the people on earth experienced no time at all. Even if local simultaneity could be established between the two reference points, Ellie's frame in the tunnels could have been in the earth bound observers past or in their future. In which case, the moment that she came back into the same frame as earth, she entered the same proper time as earth bound observers.

Perhaps I am incorrect?