There is a yahoo group dedicated to the GrandQuilter. They have great FQAs and you can get lots of help there. It sounds like she doesn't like your thread. Some machines are a little picky about needles and thread and you just have to please them. Fighting won't do any good.
Did you test on a quilt sandwich?
Don't give up so quickly - those machines need to find their sweet spot. Lots of moving parts. I haven't even made it to the "I suck" stage yet.
Have you started the threading from scratch? Maybe she's misthreaded. I'd go back to cotton thread and a regular needle (you know she takes a special needle, not just a standard size, right?) to see if she works - then go from there.
Wishing you patience.