How long have you had the horse? How often do you ride her? Do you get lessons? How often? It sounds like this is a longstanding habit that dates from before you got her. And that is not at all unusual. There are plenty of sound horses that won't pick up one lead. It sounds like you got her to pick up that lead for a little while, and then some time recently she stopped picking up that lead. How many months was the horse picking up both leads? How long has she not been picking up the one lead? What method did you use to get her to pick up the one lead? It sounds like that is no longer working, for whatever reason. And again, that could be physical, or it could be a training issue. A suggestion: don't try to get that lead 14 times. If you can't get it after three times, stop and go on to something else. Just drop it. What happens when you try 14 times is that the horse gets more and more 'confirmed' at picking up the wrong lead. Plus the horse gets sore in his muscles. If you keep doing it, you can create a problem in the stifles and hocks.