。
She said "goodnight" to me.
Literal
She [topic-は] me [to-に] goodnight [quotative-と] said.
おやすみなさい ('goodnight,' literally 'please rest') is the standard nighttime farewell — said before sleep or when parting in the late evening. The casual variant おやすみ drops the polite なさい. The phrase is morphologically a polite imperative: お+verb-stem+なさい from 休む ('rest'). Like many Japanese greetings, the literal form has fossilized into a fixed expression — nobody parses おやすみなさい as a command anymore.