how about just white girl detectives, because the idea that there are somehow no white role models/heroines for girls in hollywood doesn't even merit a response

harriet the spy
cam jansen
trixie belden
babysitters club mysteries (all seven babysitters got books - five of them were white)
american girl mysteries (samantha, kirsten, etc. - again, one black girl)

all of these i remember from my own childhood. here's a list with some newer books.

http://www.babble.com/kid/7-girls-mystery-novels-to-add-to-your-kids-book-shelves/ - looks like a couple asian girls but mostly white

i'm sure there's more

then there's the mystery series that have (white) girls and boys

boxcar children
wishbone
a to z mysteries
and on and on

what do little black girls have? alexander mccall smith? trust me white girls are in no danger of having all their representation taken away