In part it is irrational because her roots are multiethnic, like me. I have at least Scot, Irish, Mexican, Spanish, French, and Yaqui in me.
This is a wonderful example of the melting pot. Many of us in the USA are just mutts. Interesting things happen when cultures mix. It also illustrates the fluidity of racial definitions. In the end we all should be judged by the content of our character.