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Originally posted by Sicilian Babe:
...when she's getting them a drink, she sees the men bowing and scraping, and knows the truth...
Could be, however the 'bowing and scraping' of his men should come as no big surprise. She knows her husband is now Don Corleone. The 'surprise' is having the door shut in her face.

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Originally posted by Sicilian Babe:
... in the deleted scene, we see her lighting the candles in church, praying for her husband's soul...
That deleted scene is shown at the END of the saga; thereby suggesting that Kay is lighting those candles after their marriage has ended...many years after Carlo's death and after she knows what her husband has become.

Still, your theory is somewhat compelling. Can't really go along with it, though.

Apple


A wise and frugal government, which shall leave men free to regulate their own pursuits of industry and improvement, and shall not take from the mouth of labor the bread it has earned - this is the sum of good government.

- THOMAS JEFFERSON