。
She dressed up and attended the party.
Literal
She [topic-は] dressed-up [and-て] party [to-に] attended.
盛装する (せいそうする) means 'to dress up formally' — literally 'grand attire.' It implies putting on one's best clothes for a special occasion. 出席する (しゅっせきする) means 'to attend' — more formal than 出る or 行く. The te-form 盛装をして connects dressing up as the preceding action before attending.