。
She's shy around strangers.
Literal
She [topic-は] stranger-shyness [object-を] does.
人見知り (ひとみしり) originally described a developmental stage where babies become wary of unfamiliar faces, but it's now widely used for adults who are reserved or uncomfortable around people they don't know. Japanese speakers readily self-identify as 人見知り as a personality trait, and it carries less clinical weight than 'social anxiety' would in English. The をする form treats the noun as a describable behavior rather than a fixed quality.