Not much you can do but help fend off those who do end up judging you. As long as you prove to her that you're ok with being with her despite difference in race, I assume that she'll calm down eventually. Reassure her.
tell her what Bernard Baruch said to the presidents he advised in the early 1900s "Those who matter, don’t mind. Those who mind—don’t matter"
basically you have to live your life in a way that makes you happy and not worry what others thing. as long as you are living a life that you feel is in line with what you personally believe and doesn't harm others it shouldn't matter if some disagree with it. people with always have opinions about something. you just can't worry about it.
that's what i'd tell her... but i do know how she feels. i've been in interracial relationships and it can be difficult to shake the feelings of disdain people may have
In this world, people are going to judge you no matter what you do. Thankfully we live in a generation that's becoming more progressive with interracial dating. Although racism is still present, and people will look at you (not necessarily negatively), that shouldn't matter to the two of you in your own personal relationship. You just have to show her how much you like her, treat her well, and she will forget about the irrelevant people in no time.