But she's still in the "Nagato can't sleep" mode there, she didn't figure it out until the next panel.
Depends how it is interpreted maybe.
Probably you can see that panel as either she was really clueless about that until the last moment or that she was half joking to reuse the same sentence as previously with Ushio.
That's quite a striking sleep-mode...Wha!?MPMPShe's such a baby!Hello, MP-sans?Maybe Nagato-san can't sleep either?Into the Akatsuki-class' room!It's Nagato-san.