What can we do to take action against people who are being cruel to my ill (ocd) sister?

I need more info: Who is being cruel, a boss, teacher, strangers, family members? The answer would be different depending on who is the offender. Sometime to a stranger saying, "you don't know why my sister is behaving this way and what you are saying is hurtful, " is enough to embarrass them or have them ask. Many people simply do not understand mental illness and need education. Ask again if this is not enough.