We get the feeling that sometimes Janie gets overlooked. She is one of the driving forces of the story, after all. Plus, she's a strong, independently minded female character, which is somewhat unusual for a novel written by a man in 1953.
She remains a fairly consistent character throughout the novel. Lone describes her role in the gestalt as "a body to care and repair" (1.29.37) and "the part that talks" (2.12.44). So what attributes allow her to fulfill this role?
First, though, a quick note: as a child, prior to joining up with the twins and the gestalt, she too suffers from loneliness, evidenced in Part 1 when she hides in the woods after running away from home.
If you needed a friend to help you clean your room, you'd want that friend to be Janie. She cares and repairs. When Lone's gestalt lives in the shelter, she helps everyone without ever complaining or demanding repayment. She "did everything that needed doing, whatever no one else felt like doing" (2.4.2). That included fixing the battery that lights the bulbs and translates Baby's thoughts for Lone to hear.
Janie may have a sharp tongue but she's super-sweet. You know how Stern treats Gerry when the teen is a mental patient? She provides the same sort of listening to Hip when he's in a similar situation. That is, she waits for Hip to heal without prying into his business or goading him along. She prods here and there, but for the most part, she's the kindest nurse in the world.
Hip himself ponders her compassion and patience a few times, wondering why she helps him. "Janie demanded nothing. She only . . . she only waited" for him to heal, he thinks (3.7.8). She helps him heal because she thinks he deserves it for his persistence in fighting back against Gerry to track down the inventor of the anti-gravity generator. Janie also hopes he'll be able to help her and the gestalt.
It's worth noting that the mere fact of Janie taking action against Gerry by rescuing and helping to heal Hip shows her strength. After all, she is still part of the same life form as Gerry—she's the body and he's the head—but she rebels against him.
We mentioned Janie's sharp tongue. Her sweetness definitely doesn't stop Janie from having an attitude at times, especially as a clever child.
That's when she verbally takes down her mother Wima's lovers. When one of them asks her if he and the child are going to be friends, she replies, "No. You smell like Major Grenfell"—Wima's previous lover (1.15.4). Ouch, smacked down by a four year old.
It's thus no coincidence that Lone calls her the mouth of the gestalt. "I got the part that talks," he says. "That one's real good" (2.12.44).
Her attitude goes to show that she's a strong, courageous, clever, and independent woman. That is a bit uncommon for a novel published in 1953.
What's Janie's special psionic trick? In addition to telepathy, she's a telekineticist. That means she can move objects around with her mind, a power called telekinesis. She even uses it to paint at home and in the shelter. The power comes in handy for unlocking doors, recharging batteries, or any number of other tasks the gestalt needs to get done.
She is also capable, like Evelyn Kew, of sending the call that Lone responds to. When Janie is alone by the pond on the Kew property, she sends out a call that brings Lone to her briefly before he returns to his shelter. The novel says it differs from Evelyn's call in that Evelyn's wanted touching and Janie's wanted help. It describes Janie's this way:
It was a hunger, an aloneness, a wanting [...] It said without words that it was a little afraid, and burdened, and was solicitous of the burden. It said in effect who will take care of me now? (1.24.17)