Who destroyed Allison's memorial in prety little liars?

Allison is not really Allison, It is allisons twin sister Courtney. Courtney took over and pretended to be Allison. Allison killed Courtney (who everyone thought was Allison) for revenge. Then Allison started sending the girls texts since she loved to mess with people

To get into details Courtney escaped the mental institution and put Ali in her place. Ali escaped and buried Courtney alive but continued sending the messages to her 4 former best friends because like you said, Ali likes to mess with people.

If you wanna know who A is, Message Kigome 99 ^___^