Author's Note: So, I finished Shatterproof.
(By the way, WARNING: POSSIBLE SPOILERS AHEAD!)
I know they don't *technically* announce who the mole/V3 is for 2 more days, but everyone already thinks they know. So if they're right, then here's my reasoning on the decision to betray the Cahills.
It wasn't her fault.
It wasn't her fault those Cahills practically forced her to betray them. They'd tried to blow her family up! They'd abandoned them for dead. They'd left her brothers crippled. She had been forever scarred, physically and psychologically.
How could she forgive them for that? Amy spoke of uniting the branches, but it could never happen. Cahills were too pugnacious, too evil. They'd never change.
So she turned her back on her so-called "family" and found a new one—who could help her get even with them for what they'd done.
People didn't turn traitor without reason.
Author's Note: So, yeah. If the mole is Sinead, this is why I think she might do it. (By the way, anyone seen Thundercats? Sinead's reasoning behind this kind of reminds me of Pumyra's, actually. XD)
~Lily