Let’s just put on our big boy pants and tell it like it is: Dicey’s mom spends the entire book catatonic, and then she dies. Her story isn’t exactly action-packed, as she never interacts with anyone or even gets out of bed. But her influence is everywhere, and her mother and children carry the scars of her absence.
Part of Dicey’s tough-girl thing is an attempt to stave off worry. She's learned from her mother's difficulties, and she doesn't want their effects lingering for her younger siblings, either: "She wasn’t about to let that get her down. She couldn’t let it get her down—that was what had happened to Momma" (1.2). See, Liza may not be with Dicey physically, but Dicey carries the weight of the memory of her mother with her just about everywhere. But at least Dicey is learning to use that memory in a positive way. She can turn her mother's challenges into her triumphs, and that takes a very special kind of heroine.
After Liza’s death, when the children have buried her under the tree in the front yard, Gram comments on the wire holding the cracked tree together:
If the wire weren’t there, Gram had told Dicey, the tree would spread out and split, broken apart by the weight of its own growth […]
"That tree is like families," Gram had said, and Dicey, looking up now at its branches, wondered what, in that case, the wire was like. (12.3-4)
Shmoop smells a symbol. And while we think that wire could be a lot of things, we mainly think it's Liza. And before you go calling us crazy, hear us out: It’s because of Liza that Gram and the Tillerman kids are together, so she’s binding them even in death. Once Liza dies, it’s final: she’s not coming back to be their mom ever again. Even though that’s tragic, it’s also one more lesson for the Tillermans in letting go (of Liza), holding on (to each other), and reaching out (to other people who love them).