I agree with Prudie about having a meeting with the boss. But the ony way to deal with bullies is to stand up to them. She should firmly explain that she is an excellent, hard-working employee who gets along well with co-workers and customers. (If she doesn't really believe this, she should take some time convincing herself and listing positive behaviors.) Furthermore, his bullying is hindering her performance. She should then inform him that he needs to speak to her in the same manner she speaks to him--in a civil tone. She might point out that keeping an employee is much more cost-efficient than replacing one. If that doesn't work, the next time he yells at her, she should repeat this in front of her co-workers. And document everything. What has she got to lose? She'll at least have her self-respect. And probably that of her co-workers.