。
She contributed an article to the newspaper.
Literal
She [topic-は] newspaper [to-に] article [object-を] contributed.
寄稿する (きこうする) means 'to contribute (a piece of writing)' — it's a formal term used for submitting articles, essays, or opinion pieces to publications. 論文 (ろんぶん) can mean 'article, paper, thesis' depending on context; here it's a newspaper article or opinion piece. The に marks the destination publication.