If someone had called her out on her racism, that could have come across as heavy-handed. More realistically, Michelle should have said something equally racist about white women. (Technically, "white" and "latin" aren't mutually exclusive, but race is often an imprecise concept, anyway)
By "more realistically," I mean "more appropriate to the high school catfight they're trying to portray," rather than "more appropriate to the way adult professionals would act," of course.