Racial prejudice is a sin and one reason is because of the conflict it inevitably causes. It is tragic that your aunt has allowed racism to divide your family, and what she is doing is wrong.
In God's eyes, no racial or ethnic group is any better or worse than any other, and "he made every nation of men" (Acts 17:26). When Moses' brother and sister "began to talk against Moses because of his Cushite (i.e., Ethiopian) wife" (Numbers 12:1), God strongly rebuked them and struck the sister with leprosy.
At the same time, don't let your aunt's views influence your own attitudes, or cause you to react in anger or hatred toward her or other members of your family. Instead, in a gentle way, let your aunt and other relatives who are close to you know (perhaps in a letter) that you regret she has taken this position. Don't be sarcastic or rude; the Bible says, "Do not repay anyone evil for evil. ... Do not be overcome by evil, but overcome evil with good" (Romans 12:17, 21).
Most of all, pray for your aunt, and go out of your way to keep contact with your family. Over time attitudes can change with God's help.