she will want to ask what training method the trainer uses, some people are more comfortable with the clicker training, others with the old style, and still others with a different style. If she would preffer the clicker training, and she ends up with a trainer who only knows the old style, she will not be happy. Also, she will want to ask what kind of dogs the trainer has trained (I would ask this before letting the trainer know what kind of dog she is wanting trained), as different breeds tend to respond to different training methods in different ways.Such as, pit bulls; they have a high tolerence for pain, so the best way to train them is with possitive reinforcement, because even though they can tollerate pain, a pinch collar is not a good idea as this will associate pulling to another dog with pain and make them want to react to the pain with aggression. On the other hand, a German Shepard can have a pinch collar, and some (not all) need it. I avoided the pinch collar with my German Shepard by using the Halti (or Gentle Leader, they are pretty much the same thing). It also will depend on the dog and how submissive they are, so she will also want to ask if the trainer is prepared to adjust their training style to match the temperment and needs of the dog.
That would be my suggestions, I would have to think of what else to ask. I have trained all my dogs, and just now using an outside trainer for the advance work, but I also knew she viewed training like me too.