。
She sometimes stays up late.
Literal
She [topic-は] sometimes stay-up-late do.
夜ふかし (yofukashi, 'staying up late') is a noun built from 夜 ('night') plus the verbal noun of 更かす ('to make late, to let deepen'), and combines with する to form a verb. The standard kanji form is 夜更かし; this sentence uses the more casual mixed-script 夜ふかし, common in informal writing. ときどき is the everyday neutral 'sometimes,' less reflective than literary ときに and more conversational than formal 時折 — three near-synonyms calibrated to register. Casual plain form throughout makes this the kind of remark dropped between friends.