@Kulta kai  
She’s not even shivering. Must be Rule of Funny or Equestrian magic.

How does she not have hypothermia

@Joshua  
Among other things…
 
We’ll call Rule of Funny and fiction physics on this. Unless you want to think otherwise for one specific part. Simply put, aside from the cold (or lack thereof it seems), and the fact that she’s not looking the slightest bit tired (unlike that study session), not to mention she should have been too bored to continue no later than an hour in, she should have wet herself in this position, which she stayed in of her own accord no less, and though there’s no real proof against this, the Main 6 were also locked up by Starlight for the same amount of time and there were never any puddles nor signs of desperation so clearly they never had to pee once for two days either, this kind of thing happens all the time in fiction, not just MLP.
 
Maybe Equestrian magic prevented all the realistic consequences of this but even so, how did she have the patience for it? Even magic can’t explain that, only Rule of Funny.
 
Someone else pointed out too, if the snowball fight was planned two days in advance, why did Pinkie choose today to try to take the souffle to Rarity instead of taking part in the snowball fight herself? You’d think she’d be really excited for this, yet apparently she forgot.

@Joshua  
Or maybe it’s Equestrian magic!

What I find amazing is she managed to go two days like that and not die from hypothermia. Then again, this is just a cartoon.