Well this is weeds and from weeds previous storys we know they like to interfere with that damn new child. I bet it's someone related in some way to the mexican dad of the child, all we ever got was 'he died in jail' mhm surree.
Doug's gay son shot her. For stealing his dad.
In all seriousness, I'm not sure, at all. Maybe it was that guy's son, the ponzi scheme guy, maybe it was the ponzi scheme guy. But I was pretty surprised at the ending of this and The Big C.