I wonder what they argued about.
I don't know, what do young, or even somewhat older ladies usually argue about? Normally money, or a guy, I'd guess a guy.
Seems like drugs were involved at least somewhat:
I really doubt it was marijuana, unless it's that synthetic "spice", or laced with something else.
And
From: http://www.ajc.com/news/news/crime-law/warrant-argument-with-cousin-preceded-cobb-girls-s/npNyk/
Maybe whatever she smoked was laced with something? Generally marijuana by itself wouldn't have quite so extreme and violent an effect AFAIK...