Hi J.-
I'm a veterinarian and behavior consultant, plus have had 3 dogs living with my daughter, who is two. My biggest advice is to fully establish "the rules" before the baby is born. That includes self control exercises for the pup, like a "wait" command before eating, going through doors, getting treats or toys. And basic leadership exercises like not being allowed on furniture or beds, and making the dog perform a command before getting anything she wants. It is really important that she respect you as a leader- to dogs, leaders eat first, go through doors first, sit above the rest of the pack, and control all resources (toys, food etc) I would recommend not leaving dog toys all over the floor- when this is done dogs think everything on the floor is theirs. Establish a toy box for the dog and give her one or two toys from it at a time. A "drop" command is also very helpful. To do this, start by offering a treat in exchange for whatever the dog has in her mouth, this way she learns when she gives something up, something better comes along.
As far as puppy mouthiness, she needs to learn that when she uses her mouth on people, all fun stops. Tell her "no" turn your back and ignore her, even if she jumps up, barks, etc. Leave the room if you have to. The lesson for your dog is that bad behavior makes people go away. This works much better than pushing the dog off, or getting into a physical battle over it. If you are consistent, the mouthing and nipping will stop, although it might get a little worse when you first start doing this.
I used a baby doll in a swaddle to teach my dog to stay off and out of my space. Use praise for calm behavior and offer an alternative, like a chew toy, where she can sit at your feet and get attention while you are holding the baby. When the baby arrives, try to only give the dog attention when the baby is present. This is a little counterintuitive, because it's much easier to give a dog attention without baby there. But is important for the pup not to see the baby as "competition" and have a positive association with the baby. Lots of exercise will help the pup be more relaxed- although this is tough with the exhaustion of a new baby, a puppy playgroup once in awhile or dog park. When people ask how they can help after baby arrives, suggest walking the dog for you! A tired dog is a much more well-behaved dog.
It takes a lot of management at first, but it will pay off. Hope this helps! A private trainer session once baby arrives could really be invaluable. Make sure to find someone who uses positive reinforcement and get references.