Symbolism, Imagery, Allegory
When Wendy moves to California, she soon meets Garrett's girlfriend Carolyn, who lives on a cactus farm. Carolyn immediately tells Wendy that she reminds her of a cactus—and that's why Carolyn likes her so much:
The thing about cacti, Carolyn had told her. They're tough little devils. They live on dirt mostly. It's harder than hell to kill a cactus. But just because they've got all these spines and they aren't likely to keel over and die doesn't mean they don't appreciate a little babying and know-how. They're tough, but they've got needs, just like every other living thing. You have to pay attention. (20.117)
Wendy is like a cactus herself because she's tough despite all the horrible things she's been through—she's survived her mother's death and the trauma of moving across the country and starting her life anew—but that doesn't mean that she's impervious to hurt. It might take a lot to knock her down, but she still needs a bit of gentleness and TLC.
Carolyn and Garrett both know Wendy is resilient and tough, but they also know she needs them to be waiting in the wings, ready to catch her if she falls. And that's just what they give her while she stays with them in California: a safe space where she can heal and find herself without too much interference. They take care of her like their own little cactus. And in the end, she starts to thrive.