'Astonishing' and 'unfathomable' are interchangeable when reacting to Guest's various predicaments.
This is why she is so funny.
At no point has it dawned on the thick duck that telling whoppers on top of fibs is just creating yet more work for her feeble brain to try and collate all these confabulations into some sort of a coherent order so she can continue to grift her way through life.