..why?….context is the key!
..I know what you are trying to say, but you didn’t explain it well!
Calling some one a white girl can be offensive in the way that you are judging some one’s way of life. You are putting them in a category that is a stereotype. For example, when you hear people that “asians are good at math” that is a stereotype. A girl maybe wearing Uggs and drinking Starbucks (a “white girl” characteristic that some one invented) but that does not mean she has other “white girl” characteristics. I find this saying to be a very judgmental comment.
I hope this explains what my Race Card was trying to say!