Someone who's whiny, petty, and passive-aggressive and won't stand up for him/herself when shit's going down, but will be perfectly happy to stab you in the back when you least expect it. Very distinct from a regular bitch.
No, I don't think you're a little bitch because you're a girl. I think you're a little bitch because you're a sniveling rat who I can't trust with a weather report, never mind something important.
A term of endearment (a phrase used to address and/or describe a person). To put "little" in front of anything (aka little shit, little bitch, little cunt etc.) also lessens the harshness of the name calling.
You little bitch, you!, You're a handy little bitch to have around!