Never read the book but I saw the 70's film. Yes, I think in a weird messed up way I was rooting for her. She got knocked down, humiliated and repressed to the point of blowing up and making a massacre. Not mentioning her mom was just all sorts of fucked up in the head.
In Heathers I always JD should have blown up the school at the end and just walked away.
Her perception was incorrect. She was traumatized and thought everyone was laughing at her when really only those couple of shitty girls were laughing and everyone else was actually disgusted by the prankers and felt bad for Carrie. So she killed a lot of people who never did anything wrong or weren't bad people.
I definitely rooted for Carrie. She was the underdog, I think I kind of identify with her. I was an outcast in high school. I loved art and loved different things than what was popular. Also, my parents weren't rich, I didn't wear brand name clothes and I hung out with people I liked rather than just hanging out with people who were popular.
I think she had to destroy the school, the people were so mean to her. Building her up like that just so they could embarrass her in front of the whole school. Those kids were dicks.