Bring a level and make sure the frame is level with the floor.
Make sure the needle is seated correctly -- even a slight deviation can cause problems.
Is she using the same size needle and the same thread that you used? Bring the thread you used to use with the setup.
Do some sewing on it yourself. It may be the way she is moving the machine -- too fast, jerky, or .........
Check under the bobbin spring for lint. Take the bobbin case out and just run a pin under the spring. Jamie Wallen's video shows how to do this, plus his suggestions for adjusting tension work for any frame setup (not just longarms). Here is a link to his video:
http://www.youtube.com/watch?v=Q1mRhcquZTM
Check what batting is being used. I believe batik backing fabric can cause problems with some machines too.
Any burr along the thread path can cause a problem. Watch how the thread feeds to see if it is getting caught anywhere. Run your finger around all thread guides, around the needle hole, and take out the bobbin case and run a finger around the bobbin case and bobbin.
Also check to make sure that the bobbin is wound well (a badly wound bobbin can cause problems) and that the bobbin is not distorted (e.g., dropping a metal bobbin on the floor can cause distortion).