This is an interesting observation to make. Surely we would think that any parent would want to stop their children from experiencing "humiliation and pain," and yet the text tells us that Elena's mother does nothing to prevent her daughter from going to Eugene's house and experiencing the shock and pain of what transpires there. Let us examine the text a bit more closely to help us answer this question:
"You are forgetting who you are, Nina. I have seen you staring down at that boy's house. You are heading for humiliation and pain." My mother said this in Spanish in a resigned tone that surprised me, as if she had not intention of stopping me from "heading for humiliation and pain."
Clearly, the "resigned tone" that Elena's mother uses is important because she seems to recognise that Elena's death of innocence and coming-of-age is an event that is inevitable and beyond her control. Elena's mother, having experienced discrimination in her life, recognises that she can do nothing to prevent her daughter from realising the way that her ethnicity will cause others to treat her differently, and clearly feels that Elena has reached an age where she must confront such brutal facts for herself.