To get them to stay away, I like to start with a medium length buggy whip. They are a bit longer than a dressage whip, but not as long and unwieldy as a lunge whip. I teach them that my personal space is the length of the whip I carry. I also teach them that if I approach, they should stand so I can walk up to them, but they are not allowed to come into my space unless I ask.
Enter the field carrying the whip in a non-threatening manner, I just let it drag or tip it up and rest it over my shoulder. Head towards the horse you want, and watch for Jazzy to start coming close. When she does, step towards her, get big, growl and glare, tell her to "get back". If that isn't enough and she just stands there or pushes closer, give a sharp whack on the shoulder and drive her off. Don't just pick and peck at her, give her one good whack that means business. BE CAREFUL at this point and try not to let them surround you, because they will probably ALL spin around and take off, watch for flying hooves!
Let everything settle back down and do it again... and again, and again, until it sinks in that her bad behavior will NOT be tolerated any longer.
Good luck and be safe.