。
She slept off her hangover.
Literal
She [topic-は] sleeping hangover [object-を] cured.
二日酔い (ふつかよい, literally 'second-day drunk') is the Japanese word for a hangover. 治す (なおす, 'to cure, to fix') with 寝て ('by sleeping') creates the sequence: she cured the hangover by means of sleeping. A practical, everyday sentence.