She began drinking after her breakdown, really as a means of self-medicating the wrenching bi-polar highs and lows which followed.
Before long she realized she was unable to stop.
It's possible the agony of her addiction could have been prevented, with proactive psychiatric and medical care. Certainly her SSRI prescription has transformed her life for the better.
This though would have required parental units who were:
a) paying attention to the details of her identity and experience;
b) not convinced that the world and everyone in it was created to service their egos;
and
c) disinclined to view illness as a form of rebellion.
Proof that addiction really is determined by heredity.