I still don't trust her. And this episode amply explained why.
Friendship lessons seem to right over her head.
Not being a Starlight fan, (I still think her color-scheme is the worst) I was kinda dreading this episode. But I very much enjoyed it. I caught myself thinking, hey, maybe she is getting reformed... But her failure - right to the end - to get the point of the friendship lessons, and by extension, friendship itself, soon cured me of that notion. It's like she's had her empathy circuits disabled. Yeah, she tries hard, but she's not trying to be a friend, (because she's never grokked the concept) she's trying to be a success. So although she seems nice, she's nice because it gets her good treatment and kudos.
There's a big difference between being a nice person and being a good person. Nice people are often nice because, in the best case, they think they're supposed to, and in the worst case because it guilts people into giving the nice person whatever they want. (Oh, I just couldn't say no! She was being so nice!)
I'd much rather have a friend that was a good person with a few personality warts, than a nice person who had no real concept of what being a friend means when push comes to shove. All of the Mane Six have some, at least occasional, irritating personality flaws. Rainbow Dash is a solipsist, Applejack is sometimes painfully blunt, Rarity is a drama-queen, Twilight is OCD and for all her brains, she still exhibits fuzzy thinking sometimes, Pinkie is LOUD, and even Fluttershy - she's exasperatingly pollyanna sometimes - to the point that she can't see anything bad about the worst person/situation. (I think that's why her Flutterbat persona went over so well.)
But Starlight seems a little too nice to be true, just as her "conversion" to niceness happened too quickly. She's a survivor, and she seems to me to have donned the "cloak of niceness" to figure out how to come out on top of the ponies in her new environment. I don't think she necessarily means any harm, but her most basic instinct seems to be to be for power rather than for friendship and harmony.
But all's well that ends well. (I guess.) She did make a respectable apology...
And Pinkie made some very good faces...
And Dashie, of course, was cool.