If new carpet is a possible cause here is some information I found online. I also think that 100+ chemicals found in most carpets to make them resistant to stains, fire while being extremely long lasting can have a significant impact on health especially for animals and kids that spend a lot of time breathing and laying on the floor. This is a problem with most building materials (unless they are green) and it is absolutely astounding how toxic remodeled homes and new homes usually are. I am no expert, but since these chemicals are so incorporated into the product shampooing will probably not have any impact on the offgassing of VOC's. I also probably wouldn't trust the opinion of a carpet cleaner on this. Most use harmful chemicals to clean carpets and I doubt few are going to have a true understanding of the health concerns of carpet (if they really did, they probably would not be in that line of work). I have carpet in two rooms but it is 100% wool without any stain resisters and the treatment to meet code for fire resistance is natural additive. I realize I went off on a tangent, hopefully the links below will help some. A lot list neuro disorders in humans such as twitching one site mentioned hallucinations. I really feel for you and your girl and hope you can find answers soon. Perhaps you can search for a list of chemicals in the carpet through the manufacturer according with their concentration in the product? This might provide more information or let you know if this is a dead end.
CARPET DANGERS http://www.holisticmed.com/carpet/tc1.txt Carpet Installers Speak Out