。
She played the piano splendidly.
Literal
She [topic-は] piano [object-を] splendidly played.
みごと (見事) is a na-adjective meaning 'splendid, magnificent, masterful, brilliant.' Its adverbial form みごとに describes a performance carried out with admirable skill, often with a hint of impressed surprise. The literal kanji 見事 ('seeing thing') reflects an older sense of 'a sight worth seeing' — and the word still carries that visual connotation, equally at home praising a sword stroke, a botanical specimen, or a musical performance.