Alison's Diary

Alison's diary is a diary Alison kept before she died with all of the girls secrets in it. Mona (A) had this diary in her possesion at her "lair". This is most likely how Mona knew about all the girls secrets. When Spencer and Mona arrive at Room 2, Spencer finds this book and discovers Mona's secret due to a gum wrapper in a page and Mona offering her a stick of gum