。
Until then, she'd never been sightseeing in New York.
Literal
She [topic-は] until-now New-York [object-を] sightsaw [experience-こと-が] not-existed.
見物する ('to sightsee, to take in the sights') is one of several sightseeing verbs: 観光する ('tour'), 見物する ('view as a spectacle'), 見学する ('observe to learn'). 見物 has a slightly old-fashioned, leisurely feel, as in viewing a festival or famous landscape; the more neutral 観光 dominates modern travel discourse. The past-tense なかった shifts the experience pattern into the past perfect: 'had never X-ed before [some past reference point].'