。
She isn't married.
Literal
She [topic-は] is-not-married.
結婚 ('marriage') is a punctual event, so 結婚している takes the resulting-state reading rather than a progressive one: 'is in the state of having married' = 'is married.' The polite negative ~ていません flips the state — she is in the state of not having married. The blunter 結婚しない would mean 'doesn't marry / won't marry,' a future- or habit-flavored claim that's rarely what you mean. This is a recurring stumbling block for English learners who reach for ~ない reflexively when 'isn't' appears in their head.