Fortunately you can still buy plain white cotton underwear in the U.S., even if you're a girl! But we may be moving in the girls-are-for-decoration direction. I went looking for the plain white cotton girls' undershirts I remember seeing in the shops a few years ago, and found these:

http://www.onehanesplace.com/cgi-bin/ncommerce/ProductDisplay?prnbr=16062&cgnbr=9071000000

Almost the same, except that each has a "Dainty lace detail and satin bow".