One other thing that sometimes works is when she starts to get jiggy, stop her, back her up 8 or 10 strides then ask for the walk again. The second that she starts to jig or speed up, stop her and back her another 8 or 10 strides. I ride a lot like RD, most of the training type riding that I do is at either a long trot or a lope. My Dad always told me "When you have a horse that you are having a problem with, get on them then pick out a place on the horizon and lope them to it. When you reach that place, pick out another on the horizon and lope them to it. Then pick out another place and lope them to that one. When they kinda start having trouble keeping the lope, ease them down to a long trot and let them get their air for a minute then put them in a lope again. When you can't get them to lope anymore without just shagging their butt, you have a good start on getting their mind right."