Rainbow Dash really regrets destroying the Weather Factory. Like, a lot. It's been about a week since it happened, but she's still doing all she can to repair her reputation and have everypony stop hunting her down.
She's been given an out though, and it's pretty easy. All she has to do is fly from one end of Equestria to another, then fly back. If she wins, she's free from all moral and financial debt. If she loses, she'll have to clean up all of winter by herself for the next three years. No big deal for the fastest flyer in Equestria. Except it's a race, which also isn't that big of a deal. It's not the large amount flying that'll bother her, nor will the fact she has competition.
What bothers her is who she's racing.