If you're wondering what Twinkle—Sanjeev's wife and Stanford (ahem) English grad student extraordinaire—is like, just take a look at the lyrics to "Twinkle, twinkle little star":
"Twinkle, twinkle little star/How I wonder what you are/Up above the world so high/Like a diamond in the sky."
That's Twinkle to a T, which makes sense since that's where she gets her nickname. Twinkle is bright, cheerful, interesting, and curious.
Another way to describe Twinkle? She's "wow"—that's according to Sanjeev's coworker (TBH 99). She's the one who becomes the center of their housewarming party, leading all the guests in a scavenger hunt at their house for more hidden Christian stuff.
But you get the sense that Twinkle isn't all Crystal Light. After all, her graduate thesis is on an obscure Irish poet. We don't want to stereotype, but we're guessing that Irish poet probably isn't writing about unicorns and rainbows.
Which means Twinkle must have some kind of emotional depth. It's just hard to tell since the story's from Sanjeev's perspective.