What happens in Pretty Little Liars?

A killed a! Allison had a twin sister that had issues. She was sent away. When she cam back I forget how she steals allisons ring so she won't get sent back! She talks to allisons friends too! When allison finds out she kills her twin sister...the body the police find, since they are twins they have the same DNA. The parents believe the twin sister is Allison because of the ring. Allison tries to convince her parents but they don't listen since that's usually the sisters job,to pretend to be Allie. A is Allison. Allison is not dead.