so I own a Pitt Bull and a American bulldog figured i'd give ya my experience. Someone on here said "A responsible pit owner" and that hits the nail right on the head. You have to be aware of the dogs habits and watch and get used to the body language of the dog. You can make it work if you want to keep her around but just a couple tips and info.
First THE BAD: The major conflict you will have is the fact that you have so many other dogs. The bullies tend to challenge when young and test boundaries. If the older dog lets her be the alpha you wouldn't have much issue, but most likely this wont happen. And when she goes to challenge the elder alpha, and the alpha pushed back, she may not back down. It is their nature, to be dominate and rarely do they become submissive. Now its all dependent on the nature of the pitt, and how she responds to you and your commands. If she backs down to you when you discipline her its somewhat possible that you can keep things in check, if she is resilient to your discipline than there's your problem. The bullies are much better when its a 1-2 dog household with submissive counterparts. She may be a problem since you have 3 other dogs, especially since she is young and full of energy.
2nd, cats might be ok, but rabbit doesn't stand much of a chance. These dogs were originally intended to be hunters, mainly hogs, but instinctively she most likely go after that rabbit. If caught, fat happy pit, dead rabbit.
THE GOOD:
Your kids, the best thing about a bully breed is that with responsible upraising is that they are VERY VERY people and family orientated. If she is already taken to your younger daughters she will love them and be attached to them from here on out. As well as you and your wife being the complete alphas she will attach to all of the family quick and strong. Our pitt bull cuda is such a titty baby and wont stay in a room of my house without me or my girlfriend. she has to be by our side or on our laps 80% of the time.
Now an instinct on a pitt bull is something called "Prey Drive". This is a psychological response to certain signs of say wounded animals. Now its very far from common for most modern day pitt bulls to have a strong prey drive anymore but some dogs are more adapt to their hunting back ground. Basically this info is directed towards your baby and daughters. If they are crying (esp the baby) keep the dog away and busy elsewhere until you see how the pitty responds to this noise. If there is alot of curiosity from the dog when crying or loud high pitched screaming, watch the dog for any slight aggressive behavior, such as hair standing on end, and ears going back, if this occurs, just be safe and put the dog on a lead or just well away from the kiddos. Its most likely say 90% going to be fine, but until you know its not worth the risk.
As far as the dog dragging on the leash, she just needs training. And the training is simple but will test your nerves. You can either do this yourself or get a trainer to train the dog on how to walk on a leash. Basically all you need is a very strong 6 ft leash and very strong non plastic clasp collar. Get the dog outside and put the leash on. Keep the leash loose with about 3 ft to the dog and the other 3 ft coiled in big loops in your hand. Then start walking as soon as the dog gets 2-3 steps in front of you drop the extra 3 ft and immediately turn around and walk the opposite way. The dog will be Tugged pretty good, but it will not hurt the dog. Then when the dog turns around and gets in front of you again, change directions again. Continue this cycle until the dog starts walking with you looking at you to see what direction your going. The dog will think its a game and fun! Praise enthusiastically when the dog walks with you. Continue this training almost everyday for about 2 weeks, and it should break the dog from pulling. NOTE: you always want the leash to have slack, (unless correcting) if the dog pulls on a taught leash and gets away with it, its showing the dog positive reinforcement basically saying if the leash is tight, that means she can pull and its ok. Keep a good bit of slack on the leash floating about 4-5 inches from the ground.
So sorry about the lengthy post, but hope it helps some, feel free to ask me any questions. Pitts do have a bad rap, but majority of the time pitts are aggressive is because they have idiotic ill-responsible lazy owners. I wouldn't have any other breed than a Bully breed!
