... Ugh... It's weird. Obviously, the end result is supposed to be positive (except for Shimada-sensei).
But...I feel that's ultimately bad because of how it happened. Sumire hasn't overcome her past. She is tangled up in it. She is now resolving to move past it? Okay, I guess. In any realistic situation, that would be unlikely. The author can just hand-wave it away and say she has moved on, but in reality, after two years of isolation and failure, that would be difficult.
And then there's Ninomiya. Yes, she's regretful for what she previously did, and that's why she tried to support Sumire and did actually apologize to her. But...I wish that Sumire could just straightforwardly say to Ninomiya no, I do not accept your apology. I'm fine with Sumire trying to move on, but Ninomiya doesn't deserve to feel the relief of thinking that she was forgiven.
Ninomiya should just accept that she was horrible, and even if she tries, she can't always be forgiven. That would be better character development.