Wow.
I have a pit mix myself, and the last thing I want him to do is become dog aggressive. He can hold his own if someone threatens us - but generally he's just trying to get other dogs/people away from me.. and isn't trying to throw down a fight.
Usually, I'm the one on hyperactive watch duty protecting HIM from other dogs, if a dog approaches us off leash (he's only walked on-leash) i will throw rocks, cross to the other side of the street or hurry my own dog home so i can go back out to try and catch the other dog (if it's friendly) to call animal control.
The best defense your dog will have as an adult is a conscientious, alert human on the other end of the leash. That way if you are on the look out, your dog can relax and enjoy her walk, and trouble will not erupt for either of you.
Also as she grows older, she will grow into her personality more. She's just 6 months old right now, a teenager!, and she is learning how to be submissive to some dogs, while others will be submissive to her. This is all part of the growing up process for a dog. The best way to teach her is to socialize her in safe environments.
Also, as she grows older, you will have enough of a fight on your hands in regards to bad press and the laws that are being generated in cities, states, and countries world wide in the form of
Breed Specific Legislation (BSL). Pit bulls and Pit Mixes are routinely being targeted for laws that range from must wear a muzzle in public (Boston MA) to must pay higher insurance (all over the US) to will be confiscated and euthanized (Denver, CO).
Please don't encourage your dog to be dog aggressive... the BSL that targets our dogs are the result of people encouraging pit bulls and pit mixes to be aggressive agaisnt not only other dogs but humans as well. Each attack is another red mark against the breed which I have come to love so much.