Um, this is a strange question, I'm REALLY concerned about someone.

I don't think that girl is crazy.
あなた do need to care for yourself as well and to be honest, I am also not a very helpfull person but that has other reasons.
And I certainly won't act nice to people who hate me.
I don't think anything is wrong with her.

Perhaps she was asking out of curiosity. Though, that was mean of her to say that no one cares about you. あなた should care about yourself. Like what the other person said, don't be nice to people who are mean, hateful, spiteful etc. They don't deserve it, the best thing あなた can do with those people is to ignore them. Don't be mean back, that will only make matters worse. I know it's easier 発言しました than done but あなた should give it a try.

Again, I don't think she's crazy I just think she was curious to your behavior. She could have been a bit もっと見る polite about it. Also, it's normal to care about what people think of you, it's part of being human (everyone has their insecurities). Nevertheless, that doesn't mean あなた should let what people think または tell あなた dictate who あなた are and what あなた do. Hope this helps