I'm sorry that your dog had a seizure. I have a dog with a seizure disorder. There are a number of reasons why your dog had a seizure. There most common reason is if your dog has epilepsy. I don't know how old your dog is but epilepsy usually shows up at an early age. If your dog is a puppy, he may have epilepsy. You will need to watch your dog to see if she has anymore seizures until you can get her to a vet.
Other causes of a seizure are if your dog has another health problem, such as liver disease, kidney disease, brain tumor, distemper, lyme disease, gastrointestinal blockage, etc.. This usually occurs in older dogs. The best way to determine if your dog has a serious health problem, then your vet would have to thoroughly examine your dog, do blood work, x-rays and if necessary ultrasound or cat scan. Your dog may then be referred to a specialist who may be able to offer you better treatment options for your dog.
The less serious and more common causes of epilepsy are hypoglycemia(low blood sugar) or hyperglycemia(diabetes). If your dog had not eaten in a while, she may have had low blood sugar which could have triggered a small seizure. The best treatment if this is the reason is to give your dog something to eat. Peanut butter is a great choice because it is protein and has some sugar which will raise your dog's blood sugar levels fast. Also, you may need to feed your dog 2 small meals instead of once a day. This will also help maintain your dog's blood sugar levels. A vet can also do blood work to see if your dog has a blood sugar problem.
No matter what the cause, you need to take your dog to the vet as soon as possible. They can do a thorough exam and do tests to determine what caused your dog to have a seizure. If this is the first time your dog has had a seizure, that's good. That's a sign it may have just been a blood sugar problem. Also, if your dog has a seizure disorder, the vetcan put your dog on a medication to control them, such as phenobarbitol. My dog's seizures have been under control for years on this medication. also, mention to your vet to test your dog's liver and kidney function. Sometimes vets don't test for them because of they are not common, but should be checked in cases of a dog with seizures. It's just better to be safe.
The best thing you can do for your dog is to watch her until you can get her to a vet. If she has another seizure, hold her and comfort her. Talk to her to let her know that you are there. These things help comfort your dog and she will come out of the seizure sooner and it won't be as severe. This has worked with my dog. Hopefully she won't have another seizure.
Give your dog some extra love and attention. I hope she will be ok and have no more seizures.
Best of luck with your dog. Hope I helped.