。
She flashed a charming smile.
Literal
She [topic-は] charming smile [object-を] floated.
魅力的な微笑を浮かべた — 魅力的 (みりょくてき, 'charming, attractive') uses the ~的 suffix. 微笑を浮かべる ('to show a smile') uses 浮かべる in its 'display' sense. A literary, descriptive sentence.