She sounds like she is just trying to play. I can't say for certain because I am not there, but pits can be very vocal when they are playing and often grunt or growl. When you say lunging, is she getting close to the ground with her butt in the air, or do you just mean jumping towards you?
Have you started her on the Nothing In Life is Free program? If you do a search on google for NILF you will find some good information.
Koya behaved that way when I first got her too (only she was a year and harder to handle) and it just took sometime to teach her that she couldn't behave this way around us. When she started jumping and nipping, I would cross my arms and turn my back to her. It would take a few seconds for her to clue in that I wasn't intrested, but it did work.
Remember that she is just a pup and doesn't know any manners yet. It is up to you to teach her them. It sounds like a puppy without manners to me, but I am also not an expert. It sounds like she just needs abit of guidance in how to behave.
I am sure that you will get a lot of great advice here