Basically means bitch.
From Afro-American origin.
She's just a bi-atch
n. 1) a coloquial and more accepted version of "bitch"; 2) less offensive than bitch;3) less than a man, but more than a "bitch"; 4) the guy who may scrub the white walls on your car, even though they're already clean; so someone who's too low on the social ladder to be a man, but higher than a "bitch"; 5) the kind of mnan who says it's alright when you slam his face with a glass door, even though he knows you saw him before you opened it; see "bitch"
The most craptacular bi-atch of all time.