I think, from what you are telling us, that this horse has your number. And, as time goes on it will get worse. First, start doing groundwork and get her listening to you. Utilize your lunge whip but don't touch her with it. Get her moving her butt around by lunging half circles and doing change of direction. You are telling her what to do, she's not telling you. Work at this, even if over a few days, until she's pretty proficient at trotting and reversing when you ask. Now, take the time to put the pad on. If she stands quietly for a few seconds, remove it. Her reward for standing still. Continue doing this until she will stand quietly for several minutes. Put her away (huge reward). Resume next time only start with the saddle. Don't do it up, just place it on her back, same method as the pad. When you cinch her up, barely bring the cinch up then let it go so you might wish to tie a twine to it for your own ease. Do this in a slow rhythmic fashion. If not reaction, pull it barely snug then release immediately. If when you decide to mount and she starts swinging her hips, do your lungework for a couple of minutes. She won't learn from the first time. After the 2nd time she's starting to process cause and affect. She should "get it" by the third time, or maybe even a 4th. Mount up, sit there, ask nothing of her and dismount and put her away. Your patience now will pay huge dividends later.