Is Mona really A in Pretty Little Liars?

If You See In The First Part Of Pretty Little Liars Season One You Can See That Alison (Delaurentis) Was Very Mean To Mona Vanderwaal And Mona Used To Be Way Unpopular But She Came Back With A New Look, A New Attitude, And A Big Secret!

-Courtnee Loves Pretty Little Liars;)!
Mona was mad at Alison(Courtney) for never letting her be in the group with them and not talking to her. Mona one day took Alison's diary when all of her stuff was out on the curb she wanted to get pay back because they were not nice to her so she started sending the mean messages