。
She sewed a button onto her jacket.
Literal
She [topic-は] jacket [onto-に] button [object-を] sewed-on.
縫い付ける (ぬいつける) is a compound verb: 縫う ('to sew') + 付ける ('to attach') = 'to sew on.' The に marks where the button goes. ボタン is a loanword from Portuguese (botão), one of the oldest European borrowings in Japanese, dating to the 16th century.