There are many reasons why horses buck. It can be if they are uncomfortable too. Bucking is an evasion and its the way they sometimes tell us something is wrong. So get your saddle checked & her back checked out. I have known a horse who was desperately hungry to buck a rider off so that it could get to grass & eat! As the ladies say below, keep the routine varied with pole work and exercises and keeping her forward, in different gaits.
Leaning is often a training issue. It's worth sitting up and trying to encourage her to work from the hind end. Use poles (raised and on thr ground). Indirect upwards transitions. And try getting working from leg to hand in a light contacy
A Rubber Gag snaffle. (The kind with the rope cheekpieces so the whole bit slides up and down.) The mouthpiece itself will not be harsh on your sensitive horse, but the action will certainly make him think twice about rooting or dragging you down.
Try to keep her mind busy by sending her forward and do loads of school movements. Once you see her putting her head down turn some other direction to swap the thought of bucking onto keeping the balance. Don't go strainght for too long ;) :D
Bump your reins till she puts it up. Hard and quick.Mine does that to.
Don’t give her the reins and sit back with a hard leg on. Also, make sure she isn’t sore in her back or have saddle marks anywhere. This could be causing her discomfort and force her to buck
Have you heard of "grass reins"? don't know if they sell it in your country but works most of the time... Just don't adjust it too tight please.. And yes, I agree with Judith..
Don’t let her take the reans and when she starts to buck throw your legs by her shoulders and turn her Head in you will go in small circles and won’t fall off and after a while of after every buck doing it she will stop bucking
raise your hands & be one step in front of her. you should know when shes about to throw a buck, shut her down before she does it. use a one rein stop when you dont catch the buck before it happens.
Learn to read the signs. Her ears will be flat and her tail will be twitching. Talk with her and keep your legs on. Keep her attention with you. Change reigns or direction. Keep her mind occupied. My horse also bucks. Lunging becore I ride also helps.
Keeping her forward is key :)