hang on, she's drawn with a belly button on the last page.
shhh, just assume its obviously fake
Could be just the contours between the abdominal muscles I s'pose? Bit of a weird external detail to skimp on if you're already going to the trouble of making your android (presumably) capable of digesting food - probably with some sort of "bioreactor" powerplant - tho.
Also this AI definitely needs some work on its human interaction. Then again that's probably what it's in the school for to begin with.