... the possibility that Kenny shot Katja? She didn't seem suicidal to me, infact she seemed quite logical about the whole thing and was intent on putting Duck down.
Was she carrying a gun?
Did she have one at any point?
Didn't she object to carrying one?
Kenny and Kat seemed to be in constant disagreement. I actually think it's more likely he killed her than not, thinking that seeing as his son is dead anyway, he'd be better off on his own.