As howtheduck reminds us, Lynn would never under any circumstances kill Merv's avatar no matter how merciful that would be to mere outsiders. It isn't just that Elly must not be made a poor orphan sixty-year old woman with grandchildren. Were it only a sentimental love of her father that carried over into a need to not kill his avatar, we would merely be the unwilling witnesses to Lynn's bad taste.
What seems to be really happening is that the daddy who she loves more than anyone else disappointed her and refused to give her closure as regards her childhood. Said closure seems to entail his admitting that yes, he actually should have publicly beaten her mother into a bloody, whimpering pulp for daring to set limits on Lynn's behaviour and popping out a son to outshine her and so on and so forth. Since there was no God-damned way in Hell Merv Ridgway was going to do that because I really don't think that he thought his wife did anything wrong, we'd have to endure the latest indignity heaped upon poor old Jim were the strip still a going concern.