Thank you for that information. What we have to be careful of is to never coddle or soft talk a dog that is acting frightened because over time it reinforces the behavior so how you handled it in the past will show up as she ages.
At this point if you are not training daily to build confidence in her I would do this. Keep in mind you are not training her to learn how to respond to a command , you are training so she always succeeds at fulfilling the command which is what builds confidence.
From that point you want to start behavior modification training so that she starts at a distance from a motor sound and is hearing the sound briefly , then gradually as she is okay then you move her closer and keep her longer. This is not something that will happen overnight if she has been like this or two years.
I might also start some desensitizing exercises by getting a CD of sounds for dogs (found on amazon) and start to play that low inside the home when she is playing with you or is very relaxed so she gets used to the sound in an environment where she feels safe. Over time up the volume little by little as long as she is not acting upset.
When she does seem upset by sounds that is the time to work her in commands so she has something else to concentrate on.
There is also a new medication out for dogs with noise phobia so you may want to talk to your vet about using this while you train.
another med that is over the counter is melatonin and that is used for anxieties as well. http://www.petplace.com/drug-library/melatonin-melatonex/page1.aspx
I would do positive training with a special reward when working around noise and for some dogs special is a toy , not food.
Training method BAT http://empoweredanimals.com/