Rabbah - “the great,” metropolis of Ammon (2Sa 12:26-30). Its destruction is foretold also in Eze 25:5; Amo 1:14, Amo 1:15.
her daughters - the towns and villages, dependencies of the metropolis (Jos 15:45).
shall ... be heir - shall possess those who possessed him. The full accomplishment of this is still future; partially fulfilled under the Maccabees (1 Maccabees 5:6).