。
She's known to everyone.
Literal
[topic-は] everyone [by-に] is-known.
知られている is the resultant-state passive of 知る ('come to know'): 'is in the state of being known.' に here marks the agent of the passive — 'known by everyone.' Compared to みんなが知っている ('everyone knows her') the passive shifts the topical frame to the woman: she is the topic, and the knowing is something done to her. This is a classic case where Japanese passives serve a topic-management function rather than a backgrounding-the-agent function as in English.