not good at all, it appears that the lower stem is rotting!! um.. shit i don't know what to do for that, i've never seen it, try using some magnesium... maybe? maybe some dolomite lime?
I'd say take a bunch of clones if u wanna save her, but if the branches coming from the nasty part are looking fine.. i'd leave it.. but if the leaves start wilting or anything happens, def chop and clone, that really blows bro