A crop or whip should be used as an extention of your hand - not a means to beat your horse. I have never hit a horse any harder than I have hit myself with a whip.
Talking to her might help - but do so when she's not already cranky from going around with her horse but, don't be surprised if it doesn't do any good.
It doesn't hurt to try, but if it's her horse, there isn't much you can do - other than snatching the crop from her and belting her with it. But, then you'd get in trouble lol