。
She is proud of her son.
Literal
She [topic-は] her own son [object-を] pride [as-に] is-thinking.
誇りに思う ('to be proud of, to regard with pride') is the standard, slightly elevated way to express pride toward someone or something. It uses the inward [X]を[Y]に思う pattern — 'regard X as Y.' Compared to 誇りにしている ('takes pride in'), 誇りに思っている is more about the subject's internal feeling than their outward attitude.