Hahhaa!! Sorry to laugh, but Petunia sounds like SUCH a typical pit bull!!
All the problems you are having are the ones ALL of us have had with our dogs, and still occasionally have.
You need to teach Petunia the "Watch me" command to get her attention outside. Pit bulls are so hard to distract when they are fixated on something!
Start off at home where there are no distractions. Great a great treat and have Petunia sit in front of you. Show her the treat, then put it behind your back
She will first look to where your hand went. Don't move, and she will then raise her head and look at you. The second she makes eye contact, say Good Girl and instantly give her the treat.
Keep practicing, and when you know she will look at you, start saying, "Look at me" just before she does. They usually catch on this pretty quickly.
You can use this when outside too, and gradually phase the treats out, or just give them randomly.
When you are outside (or anywhere) and tell her to sit and she gets up, correct her and make her sit again, but don't use the command more than once! If you do, she'll learn that she only has to obey after the 3rd or 4th time you say it. She has to learn that she may as well obey the first time, cause she is not going anywhere until she does.
When she pulls, you can also do an ABRUPT about face and walk rapidly in the other direction. Everytime you follow her as she pulls, she has won and will continue since dogs only do what works!