I think best friends are overrated, it's kind of a slap in the face to all your other friends.. I don't really classify my friends.. I just chill with some a lot more than others.
That being said, yes I'd kill her if I called her that. She'd actually beg me to.
It's either your best friend dies... or you, your best friend, and 7 billion other people die along with every other species on the planet excluding roaches and single celled organisms and what not.