How did Alison kill herself in Pretty Little Liars?

Answer 1

She didn't .

She killed her twin sister Courtney who was in a mental hospital .

One day Courtney switched with Ali and Ali was in the mental hospital .

The Pretty Little Liars didn't know Ali had a twin .

So Courtney was acting like Ali the whole time .

Courtney figured out all the pretty little liar secrets .

And wrote them in her diary . Ali was jealous and escaped from the hospital and killed Courtney .

Ali has been hiding in Jason's house the whole time .