Generally speaking WSA, I agree with you, but just as in horses, breeding does influence behavior and tendencies. That's the point of selective breeding. How they're raised, early socialization and training are certainly HUGE factors, but breeding does have its effect as well, dogs or horses. This pup's breeding is a huge question mark, but we know some lines of pitties are bred specifically to be aggressive towards other dogs. This girl may or may not be out of those lines, but it's worth considering that the battle to keep this dog dog-safe/friendly may be harder and take more work if the deck is stacked against her in this regard.
And just as a disclaimer- I have GSDs, another maligned breed, work in rescue, and happen to have a soft spot for bully breeds, so I'm not trying to be harsh or negative at all, just practical. Not all dogs are going to end up loving other dogs and being 100% trustworthy with other dogs or small animals. Far too soon to tell with this girl yet though. :)
"Pit bulls" were created to fight in the "pit" against other dogs and many "pit bulls" are still bred to be dog aggressive. Keep in mind that "pit" fighting has not been illegal long and watering down a breed's instincts to do what it was bred for takes many, many years. Just like a Border Collie was bred to herd, a Rottweiler bred to guard, a Bloodhound bred to track, a Retriever bred to retrieve, a "pit bull" was bred to fight other dogs.
With all that being said, yes, you can manage a breed's instincts up to a certain point, but after that it is completely up to the owner to not set their dog up for failure. I would never expect a Rottweiler not to guard just like I will never expect a "pit bull" not to show dog aggression or have a very high prey drive like all terriers.
Some "pit bulls" will never show an ounce of dog aggression or prey drive in their life. Some will be perfectly fine with other dogs and other animals until they hit maturity. Some will be dog aggressive or prey driven as early as 10 weeks old.
In response to human aggression...All dog breeds have the ability to be human aggressive. "Pit bulls" are no more human aggressive than Rottweilers or German Shepherds. They are however, the most popular breed in America. With that stat comes many ignorant owners. Some who breed for human aggression and some who breed for color while ignoring any mental instabilities in the dogs being bred. Most of society can not even correctly identify a "pit bull" from any other bull breed which often leads to mislabeling a dog that has bitten a human.
My advice would be to not bring your dog anywhere with other unleashed dogs. That IMHO is setting your dog up for failure. Part of managing a dog is to have complete control in any situation you put your dog in. If you can't have complete control than I suggest not putting them in that situation. Good luck with your pup.