You should call your local poison center. All major cities have such centers. For example the number of the Rocky Mountain Poison Center is (303) 739-1123.
A doctor should examine your daughter. A chest x-ray would show if she has chemical pneumonia. This along with the risk of combustion and burns are the two important acute problems. In the long run, the greatest concern is chronic, recurrent gasoline sniffing. This can lead to toxicity that causes peripheral nerve damage.
Equally important for you and your daughter is to determine why a 7 year old would have been sniffing gasoline. The first place I would look would be to older siblings or older children in the neighborhood who might have introduced her to this dangerous behavior. You should do everything in your power to prevent a recurrence.
She probably needs to see a doc and have some blood work. Liver enzymes, and kidney screening testing comes to mind, as most toxins are eliminated through the lungs, urine, and liver. I wouldn't mess around and put this off. She needs to be evaluated ASAP. A CBC (complete blood count) probably wouldn't be a bad idea either.
All labs perform these basic tests, and you could get the results very quickly. However, a doctor must order them.
Good luck.