she says that she removed the canvas from it's wooden frame and removed a corner that can be hidden by restretching the canvas onto a new frame but making the painting smaller. this is a technique that is also used in museum restoration to repair any water damage to the outside of a painting or fire damage that might distract from the main image on the canvas.

minor cracking can occur in the paint - however if you think about how many times the mona lisa has been cut and removed from it's frame (making it much smaller than leonardo intended), it doesn't really damage the painting that much... true it is some damage, but to say its been 'hacked up' is an exaggeration.