First thing to do is make sure the room temperature is below 75F. If it is not there is a possbility the seizure was caused by overheating and you should get the temp down or the others may also be at risk. Overheating causes brain swelling and seizures if it is severe.
If you are willing to have it checked out they may be able to help you make a diagnosis. If your pet is still seizing and not eating or drinking properly anti-seizure meds sometimes help. Sometimes it is diabetes, which is easy to treat in chinchillas, just don't give them any fruit, raisins, or sugar-containing foods. Also certain nutrient deficiencies, or exposure to toxins can cause it. Although the others are not effected I recommend checking the food for moisture contamination. If the hay or pellets smells damp or moldly replace it immediately. Sometimes it is a genetic condition, epilepsy, which can also be managed more easily once you've identified it. A heart problem can also account for it and may be diagnosable with blood work. There are many things that can cause the kind of seizure you describe. The bad thing is it may take blood work to diagnose that, which, may be expensive. I strongly recommend calling your vet and asking questions. Otherwise you'll just have to wait a few days, do the best you can, and see if she pulls through. Sometimes there is no hope in these kinds of cases. If you obtained this chinchilla from a breeder I also recommend calling them and explaining your situation. A reputable breeder will do their best to remove animals with genetic problems from their herds.