That is pretty twisted for sure.
Unfortunately I would make a guess that she is deriving a huge amount of personal satisfaction from the anger and frustration it is causing you.
If the items are replaceable, forget about her and move on. If she tries to provoke you further just ignore her. That will frustrate her more.
Block her from facebook don't just unfriend her, that way you can't look at her profile either and will not be able to let her deliberate attempts to wind you up any more.
Just give your son a kiss, a hug, take him down the park and forget she ever existed.