Is this legal???

I am surprised that this even happened. I know work places can deny a person to shop there or to eat at a their restaurant, but if you are applying for a job and get an interview, can the hiring manager deny you a job because you have scars on your forearms? My friend was suicidal in HS, after Senior yr, she enrolled into a hospital so they can help her. She was beyond depressed, extremely introverted, had 2 friends, and she didn't have the best life at home. 3 years later after treament, she is better than ever. She is more open, she's happier, she more motivated. BUT. During her depression era, she would cut herself. And the manager saw them and thought she would try to kill herself at work if things got stressful. She said she could cover them with make up and that she feel fine. She is in a much better place and her doctors took her off her medication And she and her body reacted fine. I understand the manager's concern, but can she deny someone employment based on some scars and their past? Even when they get help and theDrs give a thumbs up?