She wants the moon. (She is impossibly demanding.)
SOURCE: Bernstein, Jüdische Sprichwörter und Redensarten. Compare:
Er derlangt ir dos telerl fun himl. | .ער דערלאַנגט איר דאָס טעלערל פֿון הימל
He hands her the saucer from heaven. (He gives her everything she wants.)
SOURCE: Furman, Yidishe Shprikhverter un Rednsartn