If Maddy and Az are the good adults, and Sol and Ellie are the well-meaning but not-so-smart adults, then Dr. Cable must be the bad adult. (What other kinds are there?)
Dr. Cable heads up Special Circumstances, or at least the anti-Tally division of Special Circumstances. So she's in charge of blackmailing Tally into infiltrating the Smoke; she's in charge of trailing Tally to the Smoke; and she's in charge of making all the captives into nice, conforming pretties. In other words, everything bad that happens in this book is probably Dr. Cable's doing. Think Dolores Umbridge or President Snow.
Usually, we like to find some redeeming feature in our villains, but there's not much to like about Cable here. When Tally tells Cable that the runaways use hoverboards, Cable sneers like the evil principal from an '80s movie complaining about skateboards: "Of course a hoverboard. What is it about those things and miscreants?" (16.33).
When Tally is brought to her in the Smoke and makes some excuse about why she was fighting back, Cable insults her: "Self-preservation. Well, at least you're good at something" (35.14). Even Shay, when she's pretty and likes everyone, recognizes that Cable is a monster: "I know Dr. C was horrible to you" she says to Maddy (48.37).
Cable is almost a cartoonish villain,without a single redeeming quality. So, just guessing, that means that in the later books, Westerfeld will probably give her some redeeming features, just because he likes to mess with us. And, looked at from one angle, Dr. Cable helps Tally by sending her to the Smoke. That is, it's helpful to Tally to go to the Smoke since Tally learns more about how the world really works and comes to think of the Smoke as her home.
Of course, then Cable destroys the Smoke. So, that makes it about even.