。
She stood there even after the train was no longer visible.
Literal
She [topic-は] train [subject-が] visible became-not [even though-ても] there standing was.
見えなくなる combines 見える ('to be visible') with ~なくなる ('to cease to') — 'to become invisible / no longer be visible.' The ~ても ('even though / even after') adds a concessive dimension: despite the train disappearing, she remained. そこに立っていた captures the stillness of the scene — a lingering, emotionally charged image.