Use Animation Nodes add-on, it is open-source and totally free. I'd suggest a setup like this:
The node tree duplicates A then modify its scale (new y = y*(-1)). In your case, you may want to do it with x instead. I tried to sculpt A. After I mouse-released the sculpt brush, B would be updated too. In this approach, I can't sculpt the new object (so-called ...
I know it's been couple of months but still some one might find this helpful. I've been struggling with the same problem - didn't know how to flip an object along world global axis so that object might keep it's local origin orientation, just "look" to the opposite side, say from global X axis. What I came up with is I keep a parent cube at world 0....
I have two solutions
press Ctrl+M+XYZ (flip object on x/y/z axis).
place it in the desired place.
This doesn't flip the object, but it gets you a similar result.
select the couch, and then press Shift+S+2 (Cursor to selected).
Duplicate A and select the new object.
Set the transform pivot point to 3D Cursor.
press R+Z+180 (rotate ...