Did this start after a walk or going outside?
Is there any discharge from the nose?
Is she off colour or sad?
Is she eating ok?
Thanks for the extra information.
The most common cause of sudden onset, violent sneezing is a sudden irritation to the nasal cavity - often due to the presence of a froeign body. When dogs go outside and sniff around as they do, they can inhale small objects such as blades of grass, seeds etc. and these get stuck in the complicated bone structure of the nasal cavity.
Sometimes the dog's sneezing does manage to get rid of whatever is on ther, but they can continue to sneeze as a result of the irritation and inflammation.
It would be best if you could get your dog a vet exam, they may be able to grab something in the nostril with some narrow forceps, or perhaps be able to figure out if these is something still in there. If there is just residual irritation, it may resolve with anti-inflammatory treatment, or frutehr investigation may be necessary if there is a suspicion of something still stuck.
I hope this helps,
I'm afraid if the sneezing persists today, then you really need to find a vet to take her to as she may develop nosebleeds from persistent sneezing. Perhaps there is another veterinary clinic nearby that you could try?