Get her to the vet IMMEDIATELY. Anytime you have excessive drooling and regurgitation in a deep chested dog such as a Great Dane you must be VERY concerned about the possibility of gastric dilation volvulus (GDV) also called a "Bloat". This happens when the stomach gets twisted in the abdominal cavity and if not treated with quick emergency surgery, the reduced blood supply will cause permenant damage to the tissues and death. The hallmark symptoms for this condition are excessive drooling and regurgitation / vomiting. Although its impossible to say that this is the case without seeing the dog, and there are countless causes for nausea, GDV is unfortunately VERY common in Great Danes and labor contractions can very easilly set in motion these events. I cannot stress enough that this may potentially be a life threatening emergency in which the time lapse in treatment may be fatal.... Get this dog to the vet NOW.