The dominance stuff is nonsense when it comes to all dogs, not just pitbulls.
I also wouldn't follow the two week shut down necessarily as its meant for adult dogs, not pups.
You need to intervene in the interactions between the two of them if the little dog is "tormenting" him. You have said that you are worried about the pup, but it would seem that your small dog needs some work too.
Also, don't buy in to any "breed specific" advice you get-- without knowing the parents, what you have is a mutt. There's no guarantee that she even IS a Pitbull. So take her for what she is, an individual.
For now I would keep their interactions short and sweet and separate them when things get too rambunctious. Let them interact during activities and times when they are less likely to get wound up, such as when you are out on a walk.