I am sorry to hear you are worried about your Brittany. My name is Rebecca. I am a veterinarian and will do my best to help.
Is she eating, and drinking? If you check her gums, are they pink in color or pale?
Shaking and restlessness can be a sign of fever ( can you take her temperature with a thermometer?), pain, neurologic disease, or internal disease (liver, kidney, pancreas). If I could, I would start by taking her temperature, checking her gum color and pulses, testing reflexes, palpating her lymph nodes and internal organs, and trying to see if she is painful. Finding pain in dogs can be hard; they don't usually whine or moan or whimper; sometimes all you can find is slight muscle tension, shaking, not moving around as much as normal, not eating.
So I would start with a thorough exam by a veterinarian to determine where the problem is. If she is eating you could try aspirin; 1 baby aspirin per 15 to 20 pounds of body weight with food, twice daily. If she is not eating or if she vomits, do not give aspirin. Do not give any other over the counter pain medication other than aspirin.
Let me know if this helps and what other questions you have.