Here's a bit of information (don't mean to scare you, but it is rather frightening although obviously not all will apply!).
"The reasons for dogs vomiting are likely to vary according to age, breed and gender. Pups are likely to have eaten something that disagrees with them, or may have infections, or anatomical abnormalities. Some breeds, such as golden retrievers and boxers, tend to be especially sensitive to their diets. Large breeds are more prone to gastic dilation-volvulus, while rough collies and Belgian shepherds are prone to gastric neoplasia. Prostate problems in dogs and pyometra in bitches can also cause vomiting.
The length of time a dog has been vomiting can give some clues as to the cause. Dogs that suddenly start vomiting may, for example, have an infection, have eaten something they cannot digest, suffered poisoning, or have an acute abdominal problem, like pancreatitis. Dogs that have been vomiting over a longer period, and just intermittently may have inflammatory bowel disease, or chronic gastritis, or both. What the dogs produce when they vomit can also give clues. Dogs suffering from gastric irritation may vomit bile in the morning. Pyloric obstruction is linked to vomiting undigested meals. Intestinal obstruction is linked to vomiting watery matter. When a dog vomits dark blood, looking like coffee grounds, there could be intestinal inflammation, neoplasma, or benign ulcers, though fresh blood may just be linked to the action of vomiting."
The shaking could indeed be due to hypoglycaemia, which small dogs often suffer from, and should be given several small meals a day so they don't ever run short on blood sugar levels.
Has she been spayed, and if not, has she been in season recently? Unspayed bitches can be prone to pyometra, which is an infection in the womb, and can cause severe symptoms.