I've broken in a few horses and used to barrel race...when she bucks just be sure to keep her head up. Also, if she's not calming down grab the rein down fairly close (as close as you can while keeping your weight back) to the bit and get her head around so she has to do a few really tight circles. To my knowledge, she's not going to be able to buck in that position and it will get her refocused. My trainer used this as a sort of punishment - the horses don't like it but it doesn't hurt them and it gives them a chance to forget about what they were doing. As you finish the last circle (do like two or three) don't let her stop moving, make sure she walks out of it at a brisk pace and continue on as if nothing happened. You may get the one or two oddballs that will continue trying to buck, in which case you will both end up on the ground, but your filly seems much too sensible for that. She looks good!