Her nipples with get very very pink and stick out really far after a couple of weeks. She might become aggressive toward someone in your family. Within 3-4 weeks there won't be a question, it will look like she just ate a basketball.
If she is, make a little nest for her, like a cardboard box on it's side with one of the flaps taped up so the new kittens can't get out for a couple of weeks. When she is about to give birth she will get very talkative and loud! And she will be right in your face. Cats want their human with them when they give birth.
But watch for the nipples. That's what tipped me off with my cat.