Very possible, but I think it would at least be a start. It's not like the horse hasn't been rewarded for poor behavior already so at this point it wouldn't hurt. I'm not talking about giving cookies or anything like that, just verbal praise. I would go so far as scratches, but in this situation I think any potentially unbalancing or distracting movements on the rider's part should be avoided. Even a little positive reinforcement when he does something right may help. Arabs tend to respond very well to praise, other horses too, but it seems particularly effective with Arabs. I still think the OP should get help with this problem but I think she should also incorporate praise into the process. Ideally both she and the horse get additional training to solve the problem.