。
She likes blue dresses.
Literal
She [topic-は] blue dresses [subject-が] likes.
ドレスが好き demonstrates the standard 好き pattern: the liked item takes が, not を. Learners often mistakenly use を with 好き, but since 好き is an adjective (not a verb), the thing liked is the grammatical subject (が), not the object. ドレス is a loanword from English 'dress,' typically referring to formal or party dresses.