As we know, the approach that Scott Gimple is taking with the fourth season follows more closely to the comics; in the sense that what occurs in the same way, however to different characters.
This may be an interesting thought.
In the comics before his passing, Allen tells Andrea to take care of his children, not unlike the exchange between Carol and Ryan Samuels in yesterday's episode. There are lots of parallels that can be drawn between Lizzie and Mika, and Ben and Billy - being that they're siblings of the same gender and age (except in the case of Lizzie and Mika - Lizzie is slightly older). Regardless, both pairs of siblings have lost their parents and are visibly shaken by this, which leads me on to my theory:
What if Lizzie were to kill Mika? (BONUS: What if Carol/Beth kills Lizzie thereafter?)
It's an interesting topic as the events set in motion do lean towards this eventually falling into place.
There may be one or two inconsistencies with my theory, but I would appreciate your thoughts. What do you think?