Toward the end of the first season, Álex discovers Sara's notebook hidden away in a wall. Her writings and scribbles detail Sara's battle with depression and suicidal thoughts. Sara also stole a tape of Sergio murdering Flor, hiding it with her friend Marifer as insurance against any possible retaliation from César or Sergio. When Álex discovers Sara's journal, he calls Elisa to let her know they've been wrong about everything.
By the end of the second season, Álex learns that Sara had been diagnosed with schizophrenia, which she genetically inherited from her father Abel. Sara begins acting out upon learning that Abel is her birth father, and her relationships begin to implode with those around her. Shortly before her death, she's seen messing around with the knife on the boat but drops it before she can do anything. There's no denying that Marifer is the one who tampers with the parachute's harness, but the season two finale discloses that Sara was a part of a mysterious study at the Medusa Center led by Nicandro's father, Reinaldo.
In season three, we learn that Sara didn't actually die from the parachute accident as we were led to believe. Instead, she died by suicide after she stabbed herself with a knife at the Medusa Center after undergoing torturous treatment from Reinaldo in his attempts to cure schizophrenia. "You've lost what you most wanted," Sara tells Reinaldo in her final moments.