I don't know that it has been scientifically proven that dogs can tell their owners are pregnant. There are too many instants of a dog's behavior changing when the owner became pregnant to deny it. I recently found myself wondering about a lady in our dog guide puppy raising group. She is a gynecologist and takes her puppies to her office. I wonder how they react to her patients? I can't say how dogs recognize a pregnancy or how soon. Another friend keeps breeding stock for the dog guide school. She had a male Golden Retriever that would greet her females differently when they returned a couple of weeks after being bred if they took.
If you are pregnant, you need your sleep. I hope she becomes used to the idea and decides you can make it through the night without her checking you. If she keeps it up, I will try to help you find a solution.
Dogs and babies work well together if the owners are firmly established as leaders. Dogs see all the people and dogs in the household as a pack with each having their own rank in the pack and a top dog. Life is much easier if the 2 legged pack members outrank the 4 legged ones. You can learn to play the role of top dog by reading some books or going to a good obedience class. A good obedience class or book is about you being top dog, not about rewarding standard commands with a treat. Start at
Raising Your Dog with the Monks of New Skete For more on being top dog, see
http://www.dogbreedinfo.com./topdogrules.htm They have an additional page on dogs and children. You have plenty of time if you need it to correct any problems. Done right, the dog will welcome the new pack member and become its protector.