Her car is under an extended warranty so to the dealer it goes, although seldom. I'd start with the guy on 74 who has 6,000 VW's. He could either work on it or recommend someone. There's a German auto place behind the food coop too. Chris Joiner? BMW's, maybe he works on Audi too?
I'm not involved enough with the Audi to know what to look for beyond the obvious. There's probably a forum like this that has a FAQ. We've had a small hose behind the engine replaced twice and the catalytic converter replaced. And lots of 02 sensors before we discovered that Audi's don't like fuel with much ethanol in it, like at Enmark. Stayed away from Enmark and never had another problem.
TJK