It's a bit annoying when they do a kind of character development reset to get a message across. Although sometimes I wonder whether Twilight has changed at all. She still seems like being all the student.
It's like the Discord situation again where the lack of sincere acceptance and good will towards his reformation, the unwillingness to let the past be the past, drove him into Tirek's influence, and it required Fluttershy to be herself in practicing sincere kindness and forgiveness, which is her immense inner strength. It's a beautiful irony: As easily scared as Fluttershy seems, as much has she overcome some powerful deep fears. Because she carries her friendship in the heart and doesn't need to have it whacked over her head in a crisis.

Friendship is great, but it needs to come from within, and Twilight acted like someone who has no clue about friendship if it isn't sent to her from the outside. Awarding her the title "Princess of Friendship" might have been a bad idea; might get a bit to her head. (Then again, we know from all the ponies how their destination's fulfillment (the elements) often doesn't come easily.)

She should have learned from Pinkie by now that a desire to control can become unhealthy if not kept well in check. Learning that lesson is maybe one of the most valuable for cultivation of good character, of a healthy mind. The experience of "Woah, this is not what I intended!" is important to have and learn from.

Starlight Glimmer was the sane one in this episode. She was the teacher to Twilight and Trixie, who were two poles of the same mental issue.

Become aware of how the teacher in life is often not who you think it is.