She + nigger = Shigger
A word used to refer to non-African American females who try to act similar to that of a stereotypical African American. Shigger is a less commonly used insult that is akin to "wigger."
Signs of a "shigger" are considered to be a non-African American female who is speaking ebonics, wearing baggy street clothes, walking with a limp, and other stereotypical "nigger/nigga" behavior.
It is unknown if the variation of the word "nigger" is used in this case to emphasize racism towards culturally confused persons.
Similar but often ignored terms are spigger (spanish nigger), chigger (chinese nigger), and perhaps even a few others I have yet to hear. In any case of these insults, the "er" sound can be dropped and replaced with the "a" sound, resulting in wigger, spigger, and chigger becoming wigga, spigga, and chigga.
NOTE: I am black and am not defining this to be racist. Don't shoot the messenger. If insults didn't need to be defined, there would be no category for them, so don't crap yourself over it.