Tia knows that Luna needs to be helped, but can only do what she can.  Her treatment  had worked for these last few  years but Luna's time was running low.  For the sake af Equestria Tia would not let Nightmare Moon return.  But Luna will have to pay the price.  This is not a dark fiction.  It is meant to show that Luna can help herself overcome her demonds and use them to make herself whole again.

Arthtrott arrives in ponyville looking for Twilight, who he is crushing on. he met her when she was guest speaker at the U of coltgary.  She was the top MIT wizardry graduate student, and was lecturing at the magical arts course he was auditing for extracaricular credit.  He had no magical ability at the time and was too selfconscious to pursue more than just her aquaintanceship.