After Beth's death, Jo tried to assume her role as the innocent, helpful child. Especially in relation to her parents, Jo felt the need to fill the void left by Beth's goodness. Knowing how much of her parents' time was spent in "taking care" of Beth, Jo tried to submit to the same, though her parents did not feel the need to "take care" of Jo in the same way, since they had a great deal of respect for Jo's independence and self-sufficiency.
Jo felt incredibly constrained by this role, though she pursued it with her characteristic determination. It took her a while before she realized that only Beth could fill Beth's place, just as Jo was the only one who could be herself. She and her parents all had to learn to "live around the void" left by Beth's passing.