While she rested, she'd mentally argue with herself, asking if whether or not it was a good idea to leave the area she first appeared. Rarity knew how Starlight's spell worked, they could use that and the Map to bring her back home! So it didn't matter if she left. Especially when they can bring her back anytime, anywhere, right? At least that's how she understood it, still... Best to not leave anything to chance. 