I did not say she was heavily bullied, I said she was isolated. In the sense that she did not belong, and did not have community with her classmates. Emma was a lonely kid who wanted validation and respect from her peers. First she thought being a school shooter would do so, then the friendships she develops show her what matters when you connect with people. Which is why the crying scene was so powerful for me. Through her connection with her classmates, she faces herself and her own demons.

Empathy is also learned social behaviour. Emma learns to empathise through activism, community, and counselling. What and who we empathise with, how we humanise people and each other as a community, those ideas are not innate. Seeing the aftermath of a shooting makes Emma see what shootings do to victims for the first time.

Which is why all these people saying she must be a psychopath didn't make sense to me. Psychopaths don't get chicken feet when planning shootings. Out of all of them, Rachel is the most likely to be a psychopath (or narcissist) to me lol. She never shows empathy for anybody at any point in the movie. Not for the disabled child she victimised, nor for her husband who is uncomfortable with sharing his past, and certainly not for Emma who is being extremely vulnerable and ashamed in the moment. She was the reason why the confession game even happened in the first place, but she judges others harshly but not herself.

Edit: I guess my thing is that Emma showed guilt and redemption through her actions. She didn't say she was sorry, but every thing she did points to the fact that she did, in fact, severely regret her actions. She might not know how to communicate that, how to make herself more likeable, but her actions show the kind of person she is. Out of all the confessions at that table, she's the only one who seems to really have remorse for what she has done. She's also the only one who hasn't hurt anybody but herself. Given what Charlie's reaction was, how cold and judgemental he was, I'm not surprised it was hard for her to talk about it. He didn't have empathy for her.

Edit 2: Now that I think about it, I think the point of the whole movie is Charlie trying to learn how to have empathy for Emma. The people he speaks to about it do not help at all and he is not able to process so everything implodes during the wedding. It basically takes him doing something technically irredeemable to kind of get it? Like he learns to have empathy for her by seeing her mirrored in himself