。
She's famous as a singer.
Literal
She [topic-は] singer [as-として] famous is.
~として attaches a role, capacity, or status to a noun: 'as N / in the role of N.' Common pairings include 教師として ('as a teacher'), 友人として ('as a friend'), 親として ('as a parent'). Here 歌手として positions her singer-identity as the role under which she's famous — implying she might be known for other things too (acting, business, charity), but her fame is anchored in singing. 有名 ('famous') is a na-adjective that takes で when adverbial (有名で) and な when attributive (有名な人).