Depends on the story they want to tell. A female lead may be necessary, but Lori certainly isn't and hasn't been. The most important thing she has done all season is run off and crash a car and need rescuing. Made for a cool scene when she was escaping the car, but added nothing to the story.
I was thinking of Lori's odd behavior form another angle that may come across as sexist but I don't mean it that way.
How many times in real life have men interacted with women who beg them to, "tell them the truth," only in reality to regret doing so.
In the Walking Dead
Lori and Rick seem to have come to a footing of truth telling in their relationship.
Lori essentially begs Rick to 'handle Shane,' only in the last episode to freak out when Rick does.
So I was thinking in real life how this happens on a different level:
Woman tells man to tell her the, "truth."
Woman to man: "Does this dress make me look skinnier, and I want you to tell me the truth?"
Man: "You sure you want me to tell you the truth?"
Man: "No actually you don't look any skinner in that dress."
Woman: Cry, cry, cry, whine, whine, whine, "Why doesn't it? Do I look fat? Is that what you meant?"
Man: slaps his forehead and wishes he hadn't told the truth.
So in the season finale, Rick told Lori the truth and she acted as many women and for that matter men do when they don't really mean they want to hear the truth and react badly despite demanding it in the first place.
This is how people in real life interact unfortunately.