I sent a request through her website http://www.sarahmclachlan.com/ on Jan 4th 2014 and received this in the mail on Jan 28 2014, not sure if its authentic
That's definitely her authentic signature, although I cant tell if it's a pre print by your photo.
If it's not a PP print you should see ink coming through the back when held up to a light source.
I love Sarah nice success either way.