I agree with Hamish about the glow / cast but for me it is the way the light from her phone shapes her face and highlights her expression. I also like the glazed expression Meg as she drinks her Coke and the lady appearing to half turning as if top see what is going on behind her.
Thanks a lot, Pete. The light on Caiti's face is what got me thinking to take the fotie. And that "glazed" expression on Meg's face is so her--she's very creative and thoughtful and she's often in her own wee world.