Having had a little too much hard cider to drink before trying to flying home, Rainbow Dash crashed and caused quite a ruckus. While no one was hurt, a considerable amount of property damage had been inflicted. A breathalyzer test was applied, and Dash failed, being three times over the legal limit. Thus, she was arrested, taken to jail, and booked on drinking and flying, as well as said property damage. Since it was Friday, her court date was set for Monday, which meant she'd spend the weekend in jail.
Because she was still sloshed, Dash was mummified to ensure she wouldn't hurt herself or anyone else. Securely wrapped up, she was taken to the cells, put in one, and locked up for the weekend. She protested mightily, but it was no use; the guards were used to locking up ponies from all walks of life, and even a famous Wonderbolt would be treated like everyone else.
Now alone in her cell, Dash grumbles at realizing she's going to have to spend the next two days as a mummy. She struggles, but finds that not even her famed strength and athletic physique can break free of her wrappings. Thus, she begrudgingly surrenders and tries to figure out what she's going to say to the judge… that, and how she can have her PR firm repair the damage to her reputation.