Poor Jazz - hope she's ok.
For others reading this that have not experienced a grass seed - at this time of year with so many seeds about as soon as they start head shaking I'd be off to the vets. Ear infections don't come on as suddenly as this does so you will know it's a foreign body. The head shaking to try to get rid of it is constant and it is irritating and painful for your dog. Head shaking pushes the seed further in (their barbs make it travel) so getting them to a vet asap is recommended.
This happened to Jarvis on a Friday night - he was walked at 6 and at the vets at 8 with the seed being removed by sedation. It was already resting on his eardrum about to pierce it
