。
She posed for the picture.
Literal
She [topic-は] picture [for-のために] pose [object-を] took.
ポーズをとる is a hybrid expression — ポーズ from English 'pose' loaned into Japanese as a katakana noun, plus the native verb とる ('take') — that gives the idiomatic 'to strike/take a pose.' Japanese builds many of these light-verb collocations with native verbs (とる, する, つける, 出す) attached to loanword nouns. The phrase 絵のために uses N + のために to express 'for N's sake / for the purpose of N': here the painting is the beneficiary or reason for the posing. The natural setting is an artist's studio or a photo shoot; in conversational use it can also describe striking a pose for a snapshot.