I'm not familiar with the "part one" of your question, so if you've gotten similar replies please excuse my repeat -
1st - a horse absolutely knows when you are afraid, and it makes them afraid....they are very sensitive to tension, so what you give is what you get. Before you can get her to respond to you in a relaxed, cooperative manner, you must be relaxed, and meet her where she is, emotionally speaking. It is a rare horse that's just mean (they do exist, but it's usually a mental anomaly or, occasionally, a severe case of mistreatment that has lead to the horse perceiving humans as predators).
Selling her to another party before you get to the root of her misbehavior(s) is irresponsible, and besides, your issues are probably highly solveable problems. Don't give up on her until you have explored all possible avenues - you were drawn to her for some reason, and giving up a great horse can be like fighting with a good friend - if it's premature and based on misinformation, you'll regret it for the rest of your life.
Have your vet go over her from top to bottom, to eliminate any physical reasons for her misbehavior - pain can elicit all kinds of strange reactions in horses - sometimes getting you off of them is what makes the pain stop, so bucking, running away with the rider, etc. can be indications of a physical problem. A horse that is shod improperly is also a candidate for tantrums (how do we all feel when our shoes don't fit?). If there are no apparent physical issues, she may just be sour, and needs a vacation. We give our horses two weeks off every six months or so.
Ill-fitting equipment is another common cause for misbehavior. You mentioned getting a new bit - did you get one that is gentler, or more severe? A horse with a very sensitive mouth will respond to a severe bit by holding it in their teeth, rather than letting it rest on the bars of the mouth, leaving you with no steering wheel whatsoever. You might try a rubber bit if she's very sensitive. If she's hard-mouthed, try a broken snaffle or an easy pelham, with a martingale for extra control of her head.
Work on your own attitude first. You must begin with you approaching your horse with a positive, confident attitude, relaxed, and anticipating (not demanding) her cooperation. Be ready with her favorite treat - speak to her, scratch her favorite spot, and then leave her be. The idea here is to engender trust. Horses frequently misbehave because they do not believe the person caring for and riding them has their best interest at heart (horse is thinking "if they did, why would they be so tense?"). Some people have found the "clicker" method effective for horses - look at a resource specifically for horse training - horses are not dogs.
I would suggest leaving her alone, except for feeding and basic care (minimal grooming, making sure she's in overall good shape), for about two weeks. During those two weeks, choose one or two books (I've suggested the two books I've found to be the most helpful in person and horse training). Don't choose any more than that - there are many effective philosophies, but they are not necessarily compatible with one another. Contradictory theories will only serve to confuse you, at this point.
For six to eight more weeks, work her only from the ground, do not get on her back, period. The book I suggested, Yoga for Horses, offers a wonderful system for ensuring your horse is supple and balanced, ready to receive your commands. The author is a highly regarded dressage instructor, but this method has proven useful for all schools of riding. This is a methodology that requires commitment and attention to detail. It is not a quick fix. It will pay off in the long run, however. Again, lots of rewards, treats, quiet talk, and reassurance. These exercises are actually fun. Keep the sessions short, initially, because it's hard work, on you and the horse. As she begins to accept your leadership, you'll find her more and more willing to cooperate. After making progress in the "yoga classes", move on to longue-line work (you don't need a pen for this - you'll want to vary the length of the line as she makes progress, anyway, and a pen tends to have a work-furrow that the horse naturally "falls" into). At this point, I would encourage you to include a trainer in your initial workouts. Longue work for a horse is very taxing, and if the equipment is not used properly, it can exacerbate any physical problems rather than strengthening your training system. When she is following your voice and touch commands as a matter of routine, slowly begin mounted workouts. Begin with long, working walks, in an enclosed arena, so that any behavior issues can be handled quickly, without you having to contend with the fear of being out in the middle of the pasture with an unruly horse. I would absolutely include a trainer or instructor on these initial rides, and at least once a week thereafter. Even trainers need trainers. It will make you more comfortable and less apt to convey tension to your horse. Walk ONLY for 2 weeks of workouts (for a total of at least 10 sessions). Establish basic, working communication. Halt, bending, leg yield, half-pass, serpentines, circles, etc, all at the walk.
Next move on to trot - before you ask anything of her, make sure the rhythm is firmly established - a regular, one/two beat. Relaxation at trot is crucial before you ask anything of her - begin with the same exercises you worked at walk. Pay careful attention to the transition from walk to trot and back to walk. Smooth transitions are prime indicators of balance and responsiveness to rider queues.
Also, timing is everything at this stage. If you're having a particularly troublesome day, consider getting off of her and returning to a yoga or longue session. If you're having an outstanding day, keep it short. Reward her for giving you what you're asking for - if she does everything you ask in a half-hour ride, put her away with a treat and a pat. Always end on a good note.
After 3 to 4 weeks of successful walk/trot work, introduce the canter or lope, using the same principles. Then and only then, begin working with her outside the confines of the arena. The idea is to establish trust and confidence in your leadership, for both of you.
Best of luck - it can be a hard thing to rework a horse, but most of the people who have responded to the challenge with an attitude of concern and respect for their animal have found the results to be more than worthwhile.
If for some reason you and Jazz are not a match, and that does happen, you will still benefit from establishing good habits for you and her, and you can sell her with a clear conscience, knowing she is safe for another rider. Having learned some effective techniques for training your next horse,
and becoming a better rider, is well worth the time and work. Best of luck!
(PS - if you do not have the time or money to train her properly, you do need to either lease her to someone who can train her, or perhaps trade her to someone who has an older horse that has more of a track record, behavior wise.
Continuing in your current situation puts you and Jazz at risk for injury. Your first concern as her owner MUST be for her well-being.)