All jokes aside, wouldn't this make it worse? With Sakurako moving around so much when sleeping, I feel like that would just rob Himawari of sleep, making her even more tired in the mornings.
I think that's actually meant to be what's going on in that last panel, where Himawari is sitting up in bed, looking slightly bemused and startled, instead of sleeping - I assume the punchline is that Himawari just realized that instead of oversleeping, she's not going to be getting any proper sleep at all. After all, we know Sakurako stays up too late but still wakes up early to wake her friend up, while Himawari oversleeps in spite of going to sleep rather early, so if she's wide awake while Sakurako is sleeping soundly....
Or maybe I'm wrong about that.
I'm more sure that the "BLUSH" over Sakurako's head is a mistranslation, and it's supposed to be more like 'ZZZZZZZ"... at least, that's what I'm seeing in the Spanish-language version!
That would clear up part of what mystifies me about that panel. Himawari's engimatic smile is a bit harder to account for, but fun to speculate on, since there are so many different ways to read it: Hima's relying on Sakurako anyway, in spite of the reason she did this to begin with, the seemingly selfish and childish Sakurako is actually going pretty far out of her way for her friend, the two girls act like a bickering married couple anyway, and so on.