I do not think she is conscious about the whole ethnic thing, is just how things are in upper-high Mexican class people. We are all mixed if you look at our ancestry but when most of your family tree is European, you end-up being this breed of Latino - Mexican - etc that "looks European" and that actually holds an European passport. I do not like the phrasing white passing because is not a term we use in Spanish, like, never. It does not exist as a translation or with a similar cultural term.
What does exist is the concept of "Pija" in Spain or "Fresa" in Mexico, which are terms very applicable to Lou, is like "Posh" but very derogative, because Fresas tend to hang around in a bubble. You may find it interesting
https://en.wikipedia.org/wiki/Fresa_(slang)
Lou is clearly from upper-Mexican class which is less than a 1%, even if half her bags were fake when living in Mexico, it was till an OBSENE collection for a young Mexican gal. So far she made her career from sharing her bubble-fresa lifestyle and kind of worked.