"The Farewell," which features as predominantly Asian cast, tells the story of a young woman named Billi (Awkwafina) whose family decides to keep news of a terminal diagnosis from the family's elder matriarch, Billi's grandmother Nai Nai (Shuzhen Zhao).
I am doing some reading practice. But i was confused by this sentence.
" keep news of a terminal diagnosis from the family's elder matriarch"
I know the phrase means don't tell sb. something. The problem is don't tell grandmother what? whose terminal diagnosis? Billi or Grandmother?
The answer tell me is Gradmother's terminal diagnosis. But why?
Am i missing some important information?