Thanks for the additional information. I really appreciate it.
It sounds to me like Lacey is having a bit of noise phobia due to the car crusing. This is actually pretty common in dogs and I'm actually working with a new rehabilitation dog on the same issue right now.
The thing to remember about any phobia is that it will continue or even intensify if the dog is repeatedly exposed to it. Dogs have many different phobias, but the two most common are a fear of strange places (like going down the basement stairs) and noise phobias (thunderstorms or even the sound of skateboard wheels on the pavement). Without corrective measures, some dogs will even physically harm themselves in an attempt to avoid the thing they're afraid of.
Since we've already ruled out the possibility of this being a medical issue, we can skip right to trying to change her behavior through counter conditioning.
During this counter conditions, we're going to work at desensitizing her to the noise. This means we're going to use baby steps to increase your dog's confidence. Getting her enrolled in another basic obedience class will also help as this will further the bond between you and she because you'll be asking her to do things and expecting her to respond. Dogs with phobias do really well with a strong pack leader, so getting into a class where you're going to be the leader will help a great deal. Until she's over it completely, every time you hear the noise she's afraid of, make sure to reward her with both verbal cues and treats.
These techniques require patience and may take quite a bit of time, so don't expect an instant cure. Never punish a fearful pet because such actions can actually worsen her phobias and anxiety. Instead, touch her gently and speak calmly to reassure her but avoid excessive displays of concern or petting. Speak in an upbeat tone, act happy, and divert your pets attention to a treat or fun activity. Your goal is to deliver the message that the noise is no big deal.
There are a couple over-the-counter products that you could try that reduce anxiety in dogs:
Melantonin is an over-the-counter drug that can be used to treat some anxiety issues in dogs. The dose you would give would be up to 3 mg given orally whenever necessary up to every 8 hours. More information can be found here: http://www.petplace.com/drug-library/melatonin-melatonex/page1.aspx , which includes risks, warning signs to watch out for and other bits of useful information.
Try a DAP collar. These are collars that are impregnated with a man-made version of the dog appeasing pheromone, which is a pheromone that nursing bitches give off to their pups to help them feel calm and secure. It's something that humans can't smell, but it has an amazing effect on dogs with anxiety and other issues. Although you can find them at your vet's office..you can also find them online at places like Amazon.com and Ebay for much cheaper. Just make sure they're DAP brand, as they seem to work better than some other versions.
Hopefully with some time and patience, she'll learn that the outside is nothing to be afraid of, but please keep in mind that this kind of phobia is very, very hard to work with. If none of the suggestions I've offered help, you could talk to the behaviorist or get a second opinion from another vet in your area to see if they can help you get her phobia under control.
I hope this helps.