I don’t see how this party will hurt anybody’s life. Will any Mexican be killed, harassed, turned down for a job, or any other bad thing because a bunch of young girls dressed up as Mexicans for a party? Hey, if a bunch of Mexicans want to dress up as whites, have at it! Dress up as surfer dudes, rednecks, any other white stereotype. People have no sense of humor anymore.
You make a good point. All the other sororities should also be investigated for their own insensitivity; dressing up like stereotypical white girls, who have often been the butt of many off-color jokes.