Isn't the job awarded based on employers' discretion ?? If he felt he will have to deal with hijab every day of the job and he doesn't want to do it, he wouldn't have hired her.. as simple as that.
Everyone here asking for freedom, isn't it the freedom of employer whether to choose her for a job or not ?? If it is done as a government policy or if she was denied any government position because of her hijab, then you can start questioning.. but for god's sake, what a dentist want in his office or what a manager wants in her store is upto his/her discretion. By arguing against this and blaming the dentist, you are enforcing your views on him.. not the other way. He asked her to stay neutral... no religion business.. as simple as that.. If religion is so important to her, she is free to drop the job.. if the job is important, she is free to drop the hijab in the office... she has freedom to choose. that is what important.