First off, check to see if you are getting clean clearance on the rest and cables. If your arrow is hitting anything passing through then you cannot get a clean hole, ever. That is usually why, some people cannot ever get the tear they want.
Second, don't line the string up with your sight. Line it up, visually with the tip of your arrow, and set your rest to center shot. If your sight is not set to centershot lining the string to track with it will generate a fishtail. The string wants to track to center. This is the place to start.
The way you hold your bow will affect this. The way you operate your release will affect this. Your follow through will affect this. So while you can definately improve her setup, ultimately you will need to set the bow up to her.
So, if the arrows are passing through without any deflection. And your properly aligned to the center. The tiller is set correctly. The grip is light and relaxed and you are standing directly behind the paper at approximately 9-10 feet from the arrow point at full draw. So, I would move the rest approximately 1/16 of an inch to the right (toward the bow) for a right hand shooter.