Before she made her return to the other side of the portal, Twilight made sure that Princess Celestia was cool with her returning to the place where Sunset Shimmer attempted to use the power of her crown to do evil things.
"Twilight, I will let you go back to the other side of the portal but promise you will return before it closes which I believe is in ten days. I wish you nothing but the best on your return journey to this mysterious land." said Princess Celestia with a smile on her face.
"Thanks Princess. I'll write you a letter the day before my friends and I return from Boston." said Twilight.
Right after she said these words, Twilight stepped foot into the portal and was on her way back to the mysterious land where her human friends were eagerly waiting and anticipating the long waited return of the person/pony who reunited them and made them friends again.