My heart goes out to your daughter who had to endure the most ignorant comment I have ever heard from a kid's mouth about hair and appearance.
We live near a lot of families from India, and even their two year old daughters have hella thick and long straight hair. My daughters have long hair, but thin strands. So, I get a lot of "why doesn't my hair look that big or straight." I just do a lot of things that encourage them to love their hair and their different cultures. My fam is very multicutural but most of us are black. So, I have my kids around my family a lot so they can be with kids who have curly hair and skin color like mine. I also let the get to know of how I take care of my hair since I'm 100% natural. They can feel the texture, learn about the products, and get to know my styles. That has helped my girls a lot since they realize they can do a lot with their hair from wearing my styles to the type of ponytails they see their white and asian counterparts wearing if I do a braid/twist out or leave a conditioenr in to protect and define their curls.
They also take in a lot of programs where there are many different races. That helped a lot when we lived in a very snobbish area where we were the only black/biracial family within sight. Only other minority family near us was an Asian family with one kid. Needless to say, my kids didn't see anyone who looked like them at the b-day parties, playdates and parent-child groups. So, I drove across town to a YMCA in a more multicutural neighborhood for them to take classes like ballet instead of the ballet classes offered in our area. Maybe doing something like that can help your daughter embrace her beauty.
I agree with all the other ladies about styles and products and ways to get your daughter to enjoy her hair.