Downplayed: Alice shows signs of scarring, such getting angry when witnessing group practices where the goal is to eliminate one member at a time from the practice, such as musical chairs, but aside from that she's relatively optimistic and happy.
Alice has been taught by her mentors to retain her sense of optimism and hope for the future no matter what.
...However, after getting said Backstory out of the way, she goes back to her normal happy attitude.
Alice was initially very harshly affected, but has since grown to deal with the scars in a healthy manner.
Parodied: Alice lives in a Crapsack World and her constant sunny nature is an endless source of confusion and irritation for those around her.
Zig Zagged: Alice seems to whiplash from blithe unconcern to moments of depression and back again, until no one is quite sure which is her real mood and which is fake.
Averted: Alice displays an appropriate level of depression or unhappiness over the events of her life.
Enforced: "Jeez, all these Wangsty characters around are depressing, and listening to them complain about their problems just bogs up the show and takes time away from the action. We don't want that to happen here, so we'll just have Alice ignore it all."
Lampshaded: "Don't you ever feel depressed?" "Nope!"
Invoked: Alice has a lifetime supply of 'happy pills' designed specifically to prevent her from focusing on her past.
Defied: The villain tortures Alice by confronting her with all the traumatic issues of her past, forcing her to confront them.
Discussed: "If I dwelt on all the bullshit that happened to me, I'd go crazy."
Conversed: "Ah, here comes the happy ball of sunshine." "Do you think they'll cure her?" "Fat chance."
Alice is a Stepford Smiler who refuses to dwell on anything even remotely upsetting; as The Hero, she feels she can't let herself be bogged down by bad feelings, too afraid of getting caught up in feeling sorry for herself and letting others down.
Alternatively, Alice legitimately doesn't care, and, as the tragedies around her continue to pile up, viewers are shocked by her Lack of Empathy. And Alice almost becomes a sociopath.
It turns out to be a weakness, as opposed to a strength as it's usually seen.
By choosing not to angst so as not to worry her friends, her friends end up MORE worried by her acting like an emotionless robot who seemingly doesn't care about anything.
Alice's refusal to dwell on or succumb to her problems is symbolic of her strength, courage and refusal to let her past or the unpleasant things that have happened to her define as a human being or control her in the present.
Alice's untroubled facade remains untouched for so long that everyone becomes nervous that she's 1) on the verge of a mental breakdown or 2) incapable of any feeling and a murderous sociopath in the making. Either 1 or 2 is proven correct before the end of the story.
Alternatively, the above is built up and speculated on, but the end of the story plays up Alice's positively superhuman resilience as the other kind of drama.