Is there any way to prevent fatal embolism in pregnant woman?

Not really. It is very unpredictable. Amniotic fluid can escape into the maternal blood supply with separation of the placenta during labor. This is not uniformly fatal, but the mortality is very high. We cannot know which patient will have this complication. It just happens, but is also very rare. Pulmonary embolism can occur in pregnant women due to blood clots in the legs. This can be prevented.
Depends. Depends of the cause of embolism. If she is healthy and active nothing else can be done. If she has known coagulation problems or she is high risk pregnancy( morbid obesity, diabetes) medication can help decrease the risk of embolism.