A source is
Independent Porsche Repair | Repair Shops Specializing in Porsche | PCarShops but that doesn't cover reputation. Have her look up the local PCA or at least drive by the shop and see awhat cars are in the shop and what they are doing to them. Ask to see a sample PPI report. A professional shop will have a multi page standard form that guides all the items they need to check and records the values they measure.