I am training my 4 year old mare, and when I am working with her on the ground in the round pen she walks, trots, canters, stops, extends, collects and goes right, left, and backwards all with voice commands. But, when I am on her she won't canter. She is part arab, so she has this super-smooth trot that goes like 1,000 miles an hour and she does that whenever I ask her to canter. She will just keep trotting forever. And when I do get her to canter, it's only for a couple strides then she comes to a dead stop. She is very jumpy and I tried taking the end of the split reins and giving her a little tap on her hind end when she starts trotting really fast to encourage her to canter, but she kinda freaked out when I did that and she didn't canter, so it was kind of pointless. Any suggestions would be greatly appreciated.