The 25-year-old model also said internet trolls have told her to kill herself for not posting on her dad's birthday.
The siblings took the stage at the ceremony to show their support for the musical based on their father's life.
The reality TV star said staff at Provo Canyon School would beat her, force her to take unknown pills and watch her shower.
The daughter of Michael Jackson promotes her role in the "Scream: Resurrection" miniseries with a nod to the petrifying past.
The late pop star's oldest child enjoyed the pomp and circumstance amid a rare public appearance by his youngest sibling.
Did they even know Michael Jackson??
"Birthday wishes to the love of my life, the one person who showed me what passion truly was," she wrote.