Rule of Funny. As long as it's played for laughs, stuff doesn't have to make sense. Therefore, when Rainbow Dash spent two days as a snowman for a sneak attack, she didn't get hungry, tired, cold, or have to use the bathroom (which goes double because of the Cutie Map scenario and many others in fiction). Just a fun, random joke that doesn't require much thought. Because Rule of Funny.

But what if Rule of Funny didn't apply here? In a world where it didn't, Rainbow Dash is a little bit cold, hungry, and tired, and needs to change her pants. So Rarity gives her a warm bubble bath, with help from Pinkie.

Contains: Wetting, soap/washing.

As we weren't meant to take that moment too seriously, don't take this story too seriously. Appreciate the joke for what it is, and don't let my fantasies ruin the snowball fight for you. I even tagged it AU to set it apart from the canonical Rule of Funny, and rated it M just to be safe. And even if that did happen, I know that bath probably wouldn't, I pretty much shoehorned it in and made it a bath fanfic for the thousand word minimum.