Hmm...I didn't really get the sense that Twilight was jealous of Sunset Shimmer. At the time of the first EQG, Twilight was no longer Celestia's student, and was at the beginning of forging her own path as a princess. This already limited her interaction with Celestia as she started to become preoccupied with her duties as a princess, so I would doubt that she would feel threatened if Sunset resumed as Celestia's pupil. In fact, Twilight would probably be happy for her!
Twilight was doing what she thought was best for the safety of Equestria, and for Sunset. In her position, I probably would have done the same thing, considering Sunset had lost control of the magic she acquired, turned into a power hungry demon, and threatened to launch an attack on Equestria! Despite Sunset's apology, she still needed to heal and become trustworthy again, and I bet Twilight assumed that the human world was a safer place to do so. Plus, Sunset never asked to return to Equestria during her apology. Twilight also seemed to see the Human 5 as a great friendship opportunity for Sunset!
Running away from the damaged she caused in the human world and not working to fix it would not have been a good lesson for Sunset, anyway. ^^