I don't really like the generalization that all pit or pit mixes are DA. I think that it can be a reality but if she was TRULY DA she would have shown signs of this behavior by now.
I believe that people should be cautious with pitbulls because there is a possibility of DA but it's not a CERTAINTY that all pits and pit mixes are going to attack dogs. I believe also, that what you fear you can create. I refuse to allow my dog to dictate how I will live the rest of my life. If she is DA or DR then we will deal with the it through intense training. So to answer your question of crate and rotate, absolutely no. I will not allow her go get to the point where this will be necessary.
Sorry if I came off as unclear, I didn't mean that all pit and pit mixes are DA. I meant that many of the breeds that fall under the term 'pitbull' have a higher likelihood of developing DA than many other breeds. Not all of them will be DA, but they certainly are more genetically inclined to lean in that direction.
I did not say that attacking other dogs is a certainty. My sentiments were the same as yours - people with a 'pitbull' breed need to be cautious and aware of the fact that those breeds are more likely to be DA than others. It's not about creating fear, it's about people who acquire pitbulls being aware of the characteristics of the breed they get into. Just as, for example, people who get border collies need to be aware that BC's have a higher tendency than other breeds to unhealthily fixate on toys and bizarre things (lights, shadows, etc.).
Unfortunately, no matter how much you work and how intense your training is, if your dog is DA, leaving her and another dog unsupervised is irresponsible. That's like saying you will teach your 6 year old daughter to swim REALLY well (intense training! lol) so that you can leave her in the backyard to play in the pool when no one is home. Nothing bad may ever happen, but risking it is irresponsible. People who have to crate and rotate do not do so because they haven't trained their dog enough, they do it because the risk of allowing a dog who has tried to harm or kill the other dog is not worth it. People who do not leave their dogs together without direct supervision do so because they recognize that no matter how much training and proofing you do, accidents can happen, and fights between dogs can be severely damaging and fatal.
Look, I am not saying all pitties are DA. I am not saying your dog is DA. I am not saying your dog is part pittie (my reply was based off what you wrote). What I am saying is that it is important to recognize ANY dog can become DA, and that 'pitbull' breeds tend to lean that way more so than some other breeds. If you own a pittie (or any breed with a higher probability of developing DA), it is important to consider what you would do in the event that your dog no longer tolerates dog #2, which is a real possibility. And at 9 months, a dog is not fully mentally or physically mature yet. Lots of big personality changes can and do happen before a dog reaches full maturity... I know your dog seems mature now compared to not that long ago, but she really is still a puppy and may still change. Most dogs reach full maturity around 2, 2 and a half years old.