Can white girls use remy hair?

Yes. Remy hair is human hair where the cuticles on the hair are all aligned in one direction. So it gives the best look and tangles less.

Remy hair is genrally treated to change texture to straight, curly or wavy. It is also dyed to permanently change the color of the hair depending on market demands.

So there is no reason why white girls, or any other ethnicity for that matter, should not use remy hair extensions.