Raven was a shapeshifter that was given pills to stop the multiple personality disorder she had developed. Not taking them before getting on a flight, the vast number of people surrounding her overwhelmed her mind and her body, causing her brain to implode.
Raven suffered from multiple personality disorder. How much control she had over her shapeshifting power was also tied into her mental state. If her mental state was terrible, she couldn't control her shapeshifting as she would uncontrollably transform into someone she saw.