"Before you return to your friends, Twilight, we would like to give you this last gift." Luna opened her wings with a flourish.
"This glade was our hideaway. When things felt out of control, when we could hold our temper no longer, we would come to this tranquil glade in the forest. To make sure that nothing disturbed us here, we placed upon it heavy enchantments and protections. Know this: if this glade had not sensed you coming in your distressed state and felt your great need, it would have not let you approach and enter. No creature has been in this place, save for us. It is our quiet place, which we used to calm ourselves and escape from the stresses that would build. "
"In time, near the end, we had gotten so out of control that even this place could not help. Our stubbornness eventually led us to become... that Nightmare. We would not see something like this happen to you, Twilight Sparkle. Work and learn, study and play. And if you need this place again, we have set a new spell to help you teleport directly here."
"And also, we would be most grateful, if you would call upon us to talk, should you again feel so overburdened. We see so much of what we used to be in you, and we will not see again what we had become. We would rather call you friend. This is your quiet place, Twilight Sparkle, and here you are always welcome. Now come along, you have kept your friends worried long enough!"
And with that, Princess Luna teleported them both back to Twilight's library.