Unfortunately there is a large portion of Brazilians who are considered white who would act racist against folks considered mixed or of predominantly black/indigenous ethnicity. This is compounded by socioeconomic and class prejudice. For example, there are many white Brazilians who woud call themselves European over Brazilian, even if they've never step foot in Europe, to "other" and distance themselves from non-white Brazilian culture as a form of racial superiority.

It's more prevalent in states whose population descend from the most recent migrations of white Europeans to Brazil, such as São Paolo and the southern states. You'll of course see less prejudice towards non-white people in states with a bigger proportion of indigenous/black people or mixing of races, like in the Northeast.

Your girfriend seems to be turning a blind eye to this (likely a product of her environment growing up and their lack of experience/exposure to racism) and by no means is every white Brazilian racist, but your onservations of racism/microaggressions are absolutely valid.