If the bird seed has been sitting around under the bird feeder and has gotten old, it can become moldy or have fungus growing on it. This can make your dog ill. So you should really clean up under the bird feeder daily to prevent this happening. Also Dogs can contract Cryptococcosis by inhaling infectious spores that may be present in bird droppings (frequently pigeons. Animals with suppressed or immature immune systems are most at risk of contracting Cryptococcosis. It does have a tendency to strike the nervous system. Symptoms include weight loss and lethargy, and if the central nervous system has been infected you can see head tilts, back and forth eye movements, inability to blink, incoordination, circling and even seizures. Some eye problems may also occur with cryptococcosis. You can read more about this here:
Many parasites such as worms have eggs that are in the soil, so if your dog is also ingesting some soil along with the seeds, parasites can be contracted as well.
But dogs can vomit for a number of different reasons. They vomit if given an unusual (to them) treat, a change of diet can do it, if they eat too much, some vomit if they eat grass, they vomit if they don't eat sometimes, vomit if they have a throat irritation, disease can be a cause, poisoned, and various other causes.
If a dog eats enough seed, they can develop an obstruction from it as well. You can read about intestinal obstructions here:
Pepto-Bismol can be given to a dog at 1 tsp per 5 pounds every 6 hours for upset stomach, gas, or diarrhea if you feel it is not an obstruction. If your dog is still eating offer your dog a small portion of boiled chicken and rice. It is a bland food and may help your dog feel a bit better. Be sure your dog stays hydrated by drinking and if you dog is not eating today, put a drop of pancake syrup on your dog's tongue to keep the glucose level up. If your dog is still vomiting tomorrow or develops addition symptoms, I would have her seen by your vet.