I am now convinced that the σου is an ethic dative, exactly as μας is in the first and last stanzas:-
Κουράγιο, μικροκόρη μας, πού μας εγίνεις μάνα...
As Neikos wrote:-
Μας here means 'to our advantage', so omit it as Neikos says.
Since το δάκρυ & το αίμα have no σου, this fact also makes...