I have parsed some of the images for better readability. This is not a manifesto, its her personal diary.
In short, the kid was having mental issues, depression, had no one love, hated her parents, wanted to die, and finally wanted to kill others with herself. Actually she loved and idolized her teammates, other girls named Averriana, Paige, Sydney (just from reading it say "sydney is gone", did she die?) but of course they didn't love her back the way she wanted, Many pages are dedicated to wanting to be a boy, transgender and how she was born wrong, and wanted puberty blockers. Did she wanted to be a boy so the girls would love her?
This 1st image shows parts where "Everything Hurts" is repeated along with . My assumption is standard depression after being rejected by friends and family not accepting her for who she wants to be, Maybe Borderline Personality if you want to assign a medical term as she wanted love from others (but I assume she acted creepy/weird in front of them), gets very emotionally hurt from minor sources, I've seen these patterns in people with borderline personality where they keep repeating everything hurts. Did she have actual gender dysphoria for real? Dunno,
She does write her politics a little bit but not as much as wanna being transgender, girls, feeling hurt, wanting to die. It doesn't look a bit like she was politically motivated, she just wanted to be loved but couldn't, so wanted to die and kill others along with herself.
Pretty much a suicide first and murder later like most shootings.