Symbolism, Imagery, Allegory
Turtle really puts her foot in it when she points out how Sydelle uses her crutches to get attention, but in a way she's only saying what everybody else has been thinking:
I am what I am. I don't need a crutch to get attention. (12.35)
Turtle means that Sydelle uses her fake limp and her coordinated crutches—symptoms of her imaginary disease—to make sure that people notice her.
It's true, but the truth hurts.
Angela covers for Turtle by saying,
"She used the word crutch as a symbol. She meant, you know, that people are so afraid of revealing their true selves, they have to hide behind some sort of prop." (12.36)
The thing is, Angela's really not making things any better; Sydelle's use of her crutches is both literal and symbolic. Instead of trying to stay hidden, she's using the crutches to make people find her.
Crutches don't always have to be literal, though. In Chapter 12, Sydelle accuses Turtle of using her "big mouth" (12.37) as a crutch, while Angela secretly thinks that Turtle relies too much on her braid. While Sydelle's right that Turtle does hide behind her big mouth, Angela's more correct: Turtle uses her braid to interact with people in ways that are very similar to how Sydelle uses her crutches in her interactions.
Turtle almost taunts people with her braid. Sometimes it seems like her braid is begging to be pulled, but when people do pull it, she has the perfect excuse for kicking them. And we know that kicking people is something Turtle gets a perverse joy out of. Her braid also reinforces her identity as "Turtle," and it's only after she loses it that she's able to start referring to herself as "T.R."
In a neat little twist, both Turtle and Sydelle's relationship to their crutches are changed by bombings: Turtle's braid gets burnt to a crisp after the fourth bombing, and Sydelle actually gets hurt during the second bombing, which means she has to rely on—you got it—her crutches.
In fact, the bombings end up changing a lot of the characters for the better—can you think of other figurative crutches that get compromised? Who else's worldview and sense of self gets rocked by these blasts?