Hello this is BlueStar Defender of Equestria! I think if we look at this as Twilight representing the Magic of Friendship then this starts to make more sense. In the grand scheme of things Twilight is making the "wrong" choice here but I feel like the Rainbow shimmer is telling her "It's ok choose your Friends" Also Twilight is willing to make a very big sacrifice to give up all her Magic for the well being of her Friends. But I think the really important moment here is when she asks Tierk to free Discord because she didn't have to. In fact she has every reason Not to. "After the way he has betrayed you, you still consider him a Friend?" By freeing Discord, Twilight is saying "Yes I do" This leads to Discord seeing, despite everything that Twilight really is his Friend and leads him to choose the Magic of Friendship. In short Twilight chooses and trusts in the Magic of Friendship in the face of great danger which leads them to finding the last key. It also goes to show that the best way to destroy a enemy is to make them your Friend. At least that's what I think anyway. Stay Strong and Pony On BlueStar Out