I think it’s reasonable to assume that Allie grew up knowing her parents opinions on mixed relationships, and that she loves her mum and dad.
So when Michael first showed interest in her, she should have thought “Yeah, I really fancy him, but I love my parents and they would absolutely hate this.”
At their ages it’s possible that this won’t turn out to be an enduring relationship, but the relationship with her parents may never recover.
Of course children should be able to find their own way in life, and they don’t always embrace their parents attitudes, but unless she only finds black men attractive, then the easiest and most sensible thing would have been not to have started this relationship.