Yane no Shita no Artemis - Ch. 27 - The Trap

[Simpleton]

Well, it could be that she keeps some snacks and drinks in her room, and she gets bathroom breaks every few hours or so but she does not pay attention to the time passing.

For merely six days, it's still feasible-ish that she'd manage with just some sugary drinks (and reusing the bottles afterwards) - but it's pretty borderline (and unhealthy).