If you have all three invocation items and have not yet performed the invocation, the Oracle always gives you the message about going to the bottom of Gehennom and performing the invocation. If you are missing one or two of the items, she will give you a message focused on (one of) the missing items. If you have the Amulet, she will give you an otherwise unreceivable message about continuing upward through the Elemental Planes.