It seems to me like she may be using the crop a bit further than she should. I think you should talk to her about it again, & maybe explain to her how it can properly be used. & that there are other ways she can handle the situation, rather than hitting him with it. ;)
I use a crop sometimes. Not on Daytona though, 'cause she doesn't need one. But this one horse I sometimes ride, Ariel, needs it. I just use it as a training aid. It shouldn't be used to the extreme, or used in an abusive way. A crop can only do so much, she should maybe use her seat a bit more.